diff --git a/examples/dockwidgets/MyMainWindow.cpp b/examples/dockwidgets/MyMainWindow.cpp
index d7528323..cd85f1b3 100644
--- a/examples/dockwidgets/MyMainWindow.cpp
+++ b/examples/dockwidgets/MyMainWindow.cpp
@@ -49,8 +49,9 @@ static MyWidget *newMyWidget()
     }
 }
 
-MyMainWindow::MyMainWindow(KDDockWidgets::MainWindowOptions options, QWidget *parent)
-    : MainWindow(QStringLiteral("MyMainWindow"), options, parent)
+MyMainWindow::MyMainWindow(const QString &uniqueName, KDDockWidgets::MainWindowOptions options,
+                           const QString &affinityName, QWidget *parent)
+    : MainWindow(uniqueName, options, parent)
 {
     // qApp->installEventFilter(this);
 
@@ -88,6 +89,7 @@ MyMainWindow::MyMainWindow(KDDockWidgets::MainWindowOptions options, QWidget *pa
         saver.restoreFromDisk();
     });
 
+    setAffinityName(affinityName);
     createDockWidgets();
 }
 
@@ -124,6 +126,7 @@ KDDockWidgets::DockWidgetBase *MyMainWindow::newDockWidget()
 {
     static int count = 0;
     auto dock = new KDDockWidgets::DockWidget(QStringLiteral("DockWidget #%1").arg(count));
+    dock->setAffinityName(affinityName()); // optional, just to show the feature. Pass -mi to the example to see incompatible dock widgets
 
     if (count == 1)
         dock->setIcon(QIcon::fromTheme(QStringLiteral("mail-message")));
diff --git a/examples/dockwidgets/MyMainWindow.h b/examples/dockwidgets/MyMainWindow.h
index bbbd0dec..1d002321 100644
--- a/examples/dockwidgets/MyMainWindow.h
+++ b/examples/dockwidgets/MyMainWindow.h
@@ -26,7 +26,9 @@ class MyMainWindow : public KDDockWidgets::MainWindow
 {
     Q_OBJECT
 public:
-    explicit MyMainWindow(KDDockWidgets::MainWindowOptions options, QWidget *parent = nullptr);
+    explicit MyMainWindow(const QString &uniqueName, KDDockWidgets::MainWindowOptions options,
+                          const QString &affinityName = {}, // Usually not needed. Just here to show the feature.
+                          QWidget *parent = nullptr);
 
 private:
     void createDockWidgets();
diff --git a/examples/dockwidgets/main.cpp b/examples/dockwidgets/main.cpp
index 828d1260..af3a668e 100644
--- a/examples/dockwidgets/main.cpp
+++ b/examples/dockwidgets/main.cpp
@@ -58,6 +58,12 @@ int main(int argc, char **argv)
     QCommandLineOption lazyResizeOption("l", QCoreApplication::translate("main", "Use lazy resize"));
     parser.addOption(lazyResizeOption);
 
+    QCommandLineOption multipleMainWindows("m", QCoreApplication::translate("main", "Shows two multiple main windows"));
+    parser.addOption(multipleMainWindows);
+
+    QCommandLineOption incompatibleMainWindows("i", QCoreApplication::translate("main", "Only usable with -m. Make the two main windows incompatible with each other. (Illustrates (MainWindowBase::setAffinityName))"));
+    parser.addOption(incompatibleMainWindows);
+
 #if defined(DOCKS_DEVELOPER_MODE)
     QCommandLineOption noCentralFrame("c", QCoreApplication::translate("main", "No central frame"));
     parser.addOption(noCentralFrame);
@@ -88,11 +94,33 @@ int main(int argc, char **argv)
     if (parser.isSet(lazyResizeOption))
         flags |= KDDockWidgets::Config::Flag_LazyResize;
 
+    if (parser.isSet(incompatibleMainWindows) && !parser.isSet(multipleMainWindows)) {
+        qWarning() << "Error: Argument -i requires -m";
+        return 1;
+    }
+
     KDDockWidgets::Config::self().setFlags(flags);
 
-    MyMainWindow mainWindow(options);
+    MyMainWindow mainWindow(QStringLiteral("MyMainWindow"), options);
+    mainWindow.setWindowTitle("Main Window 1");
     mainWindow.resize(1200, 1200);
     mainWindow.show();
 
+    if (parser.isSet(multipleMainWindows)) {
+        // By default a dock widget can dock into any main window.
+        // By setting an affinity name we can prevent that. Dock widgets of different affinities are incompatible.
+        const QString affinity = parser.isSet(incompatibleMainWindows) ? QStringLiteral("affinity1")
+                                                                       : QString();
+
+        auto mainWindow2 = new MyMainWindow(QStringLiteral("MyMainWindow-2"), options, affinity);
+        if (affinity.isEmpty())
+            mainWindow2->setWindowTitle("Main Window 2");
+        else
+            mainWindow2->setWindowTitle("Main Window 2 (different affinity)");
+
+        mainWindow2->resize(1200, 1200);
+        mainWindow2->show();
+    }
+
     return app.exec();
 }
diff --git a/src/DockWidgetBase.cpp b/src/DockWidgetBase.cpp
index 36349185..e2c94ef0 100644
--- a/src/DockWidgetBase.cpp
+++ b/src/DockWidgetBase.cpp
@@ -99,6 +99,7 @@ public:
     void saveTabIndex();
 
     const QString name;
+    QString affinityName;
     QString title;
     QIcon icon;
     QWidget *widget = nullptr;
@@ -143,6 +144,12 @@ void DockWidgetBase::addDockWidgetAsTab(DockWidgetBase *other)
         return;
     }
 
+    if (other->affinityName() != affinityName()) {
+        qWarning() << Q_FUNC_INFO << "Refusing to dock widget with incompatible affinity."
+                   << other->affinityName() << affinityName();
+        return;
+    }
+
     Frame *frame = this->frame();
 
     if (frame) {
@@ -171,6 +178,12 @@ void DockWidgetBase::addDockWidgetToContainingWindow(DockWidgetBase *other, Loca
         return;
     }
 
+    if (other->affinityName() != affinityName()) {
+        qWarning() << Q_FUNC_INFO << "Refusing to dock widget with incompatible affinity."
+                   << other->affinityName() << affinityName();
+        return;
+    }
+
     if (isWindow())
         morphIntoFloatingWindow();
 
@@ -325,6 +338,26 @@ bool DockWidgetBase::isOpen() const
     return d->toggleAction->isChecked();
 }
 
+QString DockWidgetBase::affinityName() const
+{
+    return d->affinityName;
+}
+
+void DockWidgetBase::setAffinityName(const QString &name)
+{
+    if (d->affinityName == name)
+        return;
+
+    if (!d->affinityName.isEmpty()) {
+        qWarning() << Q_FUNC_INFO
+                   << "Affinity is already set, refusing to change."
+                   << "Submit a feature request with a good justification.";
+        return;
+    }
+
+    d->affinityName = name;
+}
+
 FloatingWindow *DockWidgetBase::morphIntoFloatingWindow()
 {
     qCDebug(creation) << "DockWidget::morphIntoFloatingWindow() this=" << this
diff --git a/src/DockWidgetBase.h b/src/DockWidgetBase.h
index a5d6c9c5..f8946e3d 100644
--- a/src/DockWidgetBase.h
+++ b/src/DockWidgetBase.h
@@ -51,6 +51,7 @@ class DockRegistry;
 class LayoutSaver;
 class TabWidget;
 class TitleBar;
+class MainWindowBase;
 
 /**
  * @brief The DockWidget base-class. DockWidget and DockWidgetBase are only
@@ -229,6 +230,30 @@ public:
      */
     bool isOpen() const;
 
+    /**
+     * @brief Sets the affinity name. Dock widgets can only dock into dock widgets of the same affinity.
+     *
+     * By default the affinity is empty and a dock widget can dock into any main window and into any
+     * floating window. Usually you won't ever need to call
+     * this function, unless you have requirements where certain dock widgets can only dock into
+     * certain other dock widgets and main windows. @sa MainWindowBase::setAffinityName().
+     *
+     * Note: Call this function right after creating your dock widget, before adding to a main window and
+     * before restoring any layout.
+     *
+     * Note: Currently you can only call this function once, to keep the code simple and avoid
+     * edge cases. This will only be changed if a good use case comes up that requires changing
+     * affinities multiple times.
+     *
+     * @p name The affinity name.
+     */
+    void setAffinityName(const QString &name);
+
+    /**
+     * @brief Returns the affinity name. Empty by default.
+     */
+    QString affinityName() const;
+
 Q_SIGNALS:
     ///@brief signal emitted when the parent changed
     void parentChanged();
diff --git a/src/MainWindowBase.cpp b/src/MainWindowBase.cpp
index 52c95ab9..4c42364b 100644
--- a/src/MainWindowBase.cpp
+++ b/src/MainWindowBase.cpp
@@ -51,6 +51,7 @@ public:
     }
 
     QString name;
+    QString affinityName;
     const MainWindowOptions m_options;
 };
 
@@ -73,6 +74,12 @@ void MainWindowBase::addDockWidgetAsTab(DockWidgetBase *widget)
     Q_ASSERT(widget);
     qCDebug(addwidget) << Q_FUNC_INFO << widget;
 
+    if (widget->affinityName() != affinityName()) {
+        qWarning() << Q_FUNC_INFO << "Refusing to dock widget with incompatible affinity."
+                   << widget->affinityName() << affinityName();
+        return;
+    }
+
     if (d->supportsCentralFrame()) {
         dropArea()->m_centralFrame->addWidget(widget);
     } else {
@@ -82,7 +89,7 @@ void MainWindowBase::addDockWidgetAsTab(DockWidgetBase *widget)
 
 void MainWindowBase::addDockWidget(DockWidgetBase *dw, Location location, DockWidgetBase *relativeTo, AddingOption option)
 {
-     dropArea()->addDockWidget(dw, location, relativeTo, option);
+    dropArea()->addDockWidget(dw, location, relativeTo, option);
 }
 
 QString MainWindowBase::uniqueName() const
@@ -100,6 +107,26 @@ MultiSplitterLayout *MainWindowBase::multiSplitterLayout() const
     return dropArea()->multiSplitterLayout();
 }
 
+void MainWindowBase::setAffinityName(const QString &name)
+{
+    if (d->affinityName == name)
+        return;
+
+    if (!d->affinityName.isEmpty()) {
+        qWarning() << Q_FUNC_INFO
+                   << "Affinity is already set, refusing to change."
+                   << "Submit a feature request with a good justification.";
+        return;
+    }
+
+    d->affinityName = name;
+}
+
+QString MainWindowBase::affinityName() const
+{
+    return d->affinityName;
+}
+
 void MainWindowBase::setUniqueName(const QString &uniqueName)
 {
     if (uniqueName.isEmpty())
diff --git a/src/MainWindowBase.h b/src/MainWindowBase.h
index 111992a0..aa9a60a7 100644
--- a/src/MainWindowBase.h
+++ b/src/MainWindowBase.h
@@ -100,6 +100,29 @@ public:
     ///@brief returns the MultiSplitterLayout.
     MultiSplitterLayout* multiSplitterLayout() const;
 
+    /**
+     * @brief Sets the affinity name. Dock widgets can only dock into main windows of the same affinity.
+     *
+     * By default the affinity is empty and a dock widget can dock into any main window. Usually you
+     * won't ever need to call this function, unless you have requirements where certain dock widgets
+     * can only dock into certain main windows. @sa DockWidgetBase::setAffinityName().
+     *
+     * Note: Call this function right after creating your main window, before docking any dock widgets
+     * into a main window and before restoring any layout.
+     *
+     * Note: Currently you can only call this function once, to keep the code simple and avoid
+     * edge cases. This will only be changed if a good use case comes up that requires changing
+     * affinities multiple times.
+     *
+     * @p name The affinity name.
+     */
+    void setAffinityName(const QString &name);
+
+    /**
+     * @brief Returns the affinity name. Empty by default.
+     */
+    QString affinityName() const;
+
 protected:
     void setUniqueName(const QString &uniqueName);
 
diff --git a/src/private/DropArea.cpp b/src/private/DropArea.cpp
index bac59bea..0fb850b3 100644
--- a/src/private/DropArea.cpp
+++ b/src/private/DropArea.cpp
@@ -26,6 +26,7 @@
 #include "Config.h"
 #include "DropIndicatorOverlayInterface_p.h"
 #include "FrameworkWidgetFactory.h"
+#include "MainWindowBase.h"
 
 // #include "indicators/AnimatedIndicators_p.h"
 #include "WindowBeingDragged_p.h"
@@ -109,6 +110,9 @@ void DropArea::addDockWidget(DockWidgetBase *dw, Location location, DockWidgetBa
         return;
     }
 
+    if (!validateAffinity(dw))
+        return;
+
     Frame *frame = nullptr;
     Frame *relativeToFrame = relativeTo ? relativeTo->frame() : nullptr;
 
@@ -158,8 +162,22 @@ bool DropArea::contains(DockWidgetBase *dw) const
     return dw->frame() && m_layout->contains(dw->frame());
 }
 
+QString DropArea::affinityName() const
+{
+    if (auto mw = mainWindow()) {
+        return mw->affinityName();
+    } else if (auto fw = floatingWindow()) {
+        return fw->affinityName();
+    }
+
+    return QString();
+}
+
 void DropArea::hover(FloatingWindow *floatingWindow, QPoint globalPos)
 {
+    if (!validateAffinity(floatingWindow))
+        return;
+
     Frame *frame = frameContainingPos(globalPos); // Frame is nullptr if MainWindowOption_HasCentralFrame isn't set
     m_dropIndicatorOverlay->setWindowBeingDragged(floatingWindow);
     m_dropIndicatorOverlay->setHoveredFrame(frame);
@@ -220,6 +238,8 @@ bool DropArea::drop(FloatingWindow *droppedWindow, QPoint globalPos)
         break;
     case DropIndicatorOverlayInterface::DropLocation_Center:
         qCDebug(hovering) << "Tabbing" << droppedWindow << "into" << acceptingFrame;
+        if (!validateAffinity(droppedWindow))
+            return false;
         acceptingFrame->addWidget(droppedWindow);
         break;
 
@@ -241,10 +261,16 @@ bool DropArea::drop(QWidgetOrQuick *droppedWindow, KDDockWidgets::Location locat
     qCDebug(docking) << "DropArea::addFrame";
 
     if (auto dock = qobject_cast<DockWidgetBase *>(droppedWindow)) {
+        if (!validateAffinity(dock))
+            return false;
+
         auto frame = Config::self().frameworkWidgetFactory()->createFrame();
         frame->addWidget(dock);
         m_layout->addWidget(frame, location, relativeTo);
     } else if (auto floatingWindow = qobject_cast<FloatingWindow *>(droppedWindow)) {
+        if (!validateAffinity(floatingWindow))
+            return false;
+
         m_layout->addMultiSplitter(floatingWindow->dropArea(), location, relativeTo);
         floatingWindow->scheduleDeleteLater();
         return true;
@@ -261,3 +287,16 @@ void DropArea::removeHover()
     m_dropIndicatorOverlay->setWindowBeingDragged(nullptr);
     m_dropIndicatorOverlay->setCurrentDropLocation(DropIndicatorOverlayInterface::DropLocation_None);
 }
+
+template<typename T>
+bool DropArea::validateAffinity(T *window) const
+{
+    if (window->affinityName() != affinityName()) {
+        // Commented the warning, so we don't warn when hovering over
+        //qWarning() << Q_FUNC_INFO << "Refusing to dock widget with incompatible affinity."
+                   //<< window->affinityName() << affinityName();
+        return false;
+    }
+
+    return true;
+}
diff --git a/src/private/DropArea_p.h b/src/private/DropArea_p.h
index a2850622..5ff53d04 100644
--- a/src/private/DropArea_p.h
+++ b/src/private/DropArea_p.h
@@ -68,13 +68,18 @@ public:
 
     bool checkSanity(MultiSplitterLayout::AnchorSanityOption o = MultiSplitterLayout::AnchorSanity_All);
     bool contains(DockWidgetBase *) const;
+
+    QString affinityName() const;
 private:
     Q_DISABLE_COPY(DropArea)
     friend class Frame;
     friend class TestDocks;
     friend class DropIndicatorOverlayInterface;
     friend class AnimatedIndicators;
+    template <typename T>
+    bool validateAffinity(T *) const;
     bool m_inDestructor = false;
+    QString m_affinityName;
     DropIndicatorOverlayInterface *m_dropIndicatorOverlay = nullptr;
 };
 }
diff --git a/src/private/FloatingWindow.cpp b/src/private/FloatingWindow.cpp
index 70829d2c..24078b69 100644
--- a/src/private/FloatingWindow.cpp
+++ b/src/private/FloatingWindow.cpp
@@ -122,7 +122,7 @@ FloatingWindow::FloatingWindow(MainWindowBase *parent)
     m_layoutDestroyedConnection = connect(ms, &MultiSplitterLayout::destroyed, this, &FloatingWindow::scheduleDeleteLater);
 }
 
-static MainWindowBase* hackFindParentHarder(MainWindowBase *candidateParent)
+static MainWindowBase* hackFindParentHarder(Frame *frame, MainWindowBase *candidateParent)
 {
     // TODO: Using a parent helps the floating windows stay in front of the main window always.
     // We're not receiving the parent via ctor argument as the app can have multiple-main windows,
@@ -137,10 +137,30 @@ static MainWindowBase* hackFindParentHarder(MainWindowBase *candidateParent)
 
     if (windows.isEmpty())
         return nullptr;
-    if (windows.size() == 1)
+
+    if (windows.size() == 1) {
         return windows.first();
-    else {
-        qWarning() << Q_FUNC_INFO << "There's multiple MainWindows, not sure what to do about parenting";
+    } else {
+        const QString affinityName = frame ? frame->affinityName() : QString();
+
+        if (affinityName.isEmpty()) {
+
+            for (MainWindowBase *window : windows) {
+                if (window->affinityName().isEmpty())
+                    return window;
+            }
+
+            qWarning() << Q_FUNC_INFO << "No window with empty affinity found";
+
+        } else {
+            for (MainWindowBase *window : windows) {
+                if (window->affinityName() == affinityName)
+                    return window;
+            }
+
+            qWarning() << Q_FUNC_INFO << "No window with affinity" << affinityName << "found";
+        }
+
         return windows.first();
     }
 #else
@@ -150,7 +170,7 @@ static MainWindowBase* hackFindParentHarder(MainWindowBase *candidateParent)
 }
 
 FloatingWindow::FloatingWindow(Frame *frame, MainWindowBase *parent)
-    : FloatingWindow(hackFindParentHarder(parent))
+    : FloatingWindow(hackFindParentHarder(frame, parent))
 {
     m_disableSetVisible = true;
     // Adding a widget will trigger onFrameCountChanged, which triggers a setVisible(true).
@@ -310,6 +330,12 @@ void FloatingWindow::updateTitleBarVisibility()
     m_titleBar->setVisible(visible);
 }
 
+QString FloatingWindow::affinityName() const
+{
+    auto frames = this->frames();
+    return frames.isEmpty() ? QString() : frames.constFirst()->affinityName();
+}
+
 void FloatingWindow::updateTitleAndIcon()
 {
     QString title;
diff --git a/src/private/FloatingWindow_p.h b/src/private/FloatingWindow_p.h
index a803f093..6f555758 100644
--- a/src/private/FloatingWindow_p.h
+++ b/src/private/FloatingWindow_p.h
@@ -109,6 +109,8 @@ public:
     void updateTitleAndIcon();
     void updateTitleBarVisibility();
 
+    QString affinityName() const;
+
 Q_SIGNALS:
     void numFramesChanged();
 protected:
diff --git a/src/private/Frame.cpp b/src/private/Frame.cpp
index 00e5b890..e744f31e 100644
--- a/src/private/Frame.cpp
+++ b/src/private/Frame.cpp
@@ -405,6 +405,15 @@ bool Frame::hasTabsVisible() const
     return alwaysShowsTabs() || dockWidgetCount() > 1;
 }
 
+QString Frame::affinityName() const
+{
+    if (isEmpty()) {
+        return {};
+    } else {
+        return dockWidgetAt(0)->affinityName();
+    }
+}
+
 DockWidgetBase *Frame::dockWidgetAt(int index) const
 {
     return qobject_cast<DockWidgetBase *>(m_tabWidget->dockwidgetAt(index));
diff --git a/src/private/Frame_p.h b/src/private/Frame_p.h
index cd3d3c6d..d42ba3d3 100644
--- a/src/private/Frame_p.h
+++ b/src/private/Frame_p.h
@@ -202,6 +202,8 @@ public:
      **/
     bool hasTabsVisible() const;
 
+    QString affinityName() const;
+
 Q_SIGNALS:
     void currentDockWidgetChanged(KDDockWidgets::DockWidgetBase *);
     void numDockWidgetsChanged();