"Split screen" means two different features on a Mac, and which one you get depends on how you start it. Here is the fast way, the full-screen way, the three and four way splits, what changes when there is a second monitor involved, and the thing that trips everyone up afterwards.
The short answer
The shortcuts
On macOS Sequoia and later every tiling position has a key combination, which is faster than any amount of dragging once you know two of them. Fn is the key labelled Globe on keyboards that have one.
One window
| Left half | Fn-Control-Left Arrow |
|---|---|
| Right half | Fn-Control-Right Arrow |
| Top half | Fn-Control-Up Arrow |
| Bottom half | Fn-Control-Down Arrow |
| Fill the screen | Fn-Control-F |
| Centre it again | Fn-Control-C |
| Undo the tile | Fn-Control-R |
Two windows in one press
These place the front window and then let you click the window that fills the rest, so a full side-by-side split costs one shortcut and one click.
| This window left, next one right | Fn-Control-Shift-Left Arrow |
|---|---|
| This window right, next one left | Fn-Control-Shift-Right Arrow |
| This window top, next one bottom | Fn-Control-Shift-Up Arrow |
| This window bottom, next one top | Fn-Control-Shift-Down Arrow |
| This window left, two stacked on the right | Fn-Control-Option-Shift-Left Arrow |
| This window right, two stacked on the left | Fn-Control-Option-Shift-Right Arrow |
The four-quadrant arrangements have no shortcut. Reach them from the menu bar under Window, Move & Resize, or by dragging windows into the corners. Apple lists the full set in its window tiling shortcut reference.
Dragging to an edge
Drag a window to the left or right edge and it takes that half; drag it into a corner and it takes that quarter. Holding Option while you drag skips the pause before the outline appears, which is worth the habit. Dragging to the top edge is the one to watch: by default that opens Mission Control rather than tiling, and you can swap that behaviour in System Settings, Desktop and Dock, under Drag windows to top of screen to enter Mission Control.
Split View: the full-screen way
This is the older feature, and it is still there. Hold the pointer over the green button in the top-left corner of a window, without clicking, then choose Full Screen and either Left of Screen or Right of Screen. macOS shows your other windows so you can click the one that fills the other half. The pair now lives in its own full-screen Space, with a thin divider you can drag to change the ratio.
The difference that matters: Split View hides the Dock, the menu bar and your desktop, and switching away with Mission Control or a trackpad swipe leaves the split parked in its own Space until you come back. Sequoia tiling keeps everything on your ordinary desktop. Pick Split View when you want the distraction-free version, tiling when you want to keep clicking other things.
Starting a split from Mission Control
Open Mission Control (Control-Up Arrow, or a three or four finger swipe up on the trackpad) and drag a window up next to another window's thumbnail at the top of the screen. Dropping it there creates a Split View Space out of the two, which beats the green button menu when both windows are already open.
Getting out of a split
For a tiled window on the normal desktop, press Fn-Control-R to put it back to the size it was, or drag it away from the edge. For full-screen Split View, hold the pointer over the green button on either window and choose Move Window to Desktop. The other window stays full screen until you do the same to it, which is the step people miss when they think Split View will not let go. Replace Tiled Window, in the same menu, swaps one side for a different app without taking the whole thing apart.
Splitting three or four ways
Split View pairs exactly two windows and always has. For three or four, use Sequoia tiling: drag each window into a different corner for quarters, or press Fn-Control-Option-Shift-Left Arrow to run the active window down the whole left side with two stacked to its right, which is the layout most people actually want on a wide screen. One tall reference window, two short ones beside it.
Split screen on a Mac with an external monitor
Two things change once a second display is plugged in.
First, a split never crosses displays. Each display has its own Spaces, so a tiled pair lives entirely on one screen. You can build a separate split on each monitor, which is the real answer to using both at once, but you cannot stretch one pair across the bezel gap.
Second, if the green button menu does nothing on the external screen, full-screen Split View is switched off for it. Turn on Displays have separate Spaces in System Settings, Desktop and Dock, which Apple documents as the requirement for using Split View on other displays. Sequoia tiling works on any display either way. If you are still setting the desk up, the Mac multi-monitor setup guide covers arrangement, scaling and which screen should hold the menu bar.
Why the green button will not split
macOS can only tile a window it is allowed to resize. Preferences panels, small utility palettes and modal dialogs are fixed size, so their tiling options are greyed out and nothing happens no matter which route you try. It is not a setting you can change; the app decides. The other two causes are the external-display one above, and an app running in full screen already, which has to come back to the desktop before it can be tiled with anything.
Stage Manager is not split screen
Stage Manager, from Control Centre, keeps one window front and centre with your other recent windows as thumbnails down the left edge. Dragging a thumbnail next to the front window groups them, which looks like a split, but it is a decluttering tool built around one focused window rather than a fixed ratio. The windows keep their own sizes instead of snapping to halves.
Third-party split-screen tools
Apps built for snapping, like Rectangle and Magnet, tile to halves and quarters from shortcuts that work back to older macOS versions, and Moom adds saved layouts on top. Since Sequoia shipped native tiling the gap is narrower than it was, and it is mostly about custom grids and per-app rules now. We go through all of them, including which ones are still worth paying for, in window snapping on Mac and the Mac window manager comparison.
What none of these survive
Split View, Sequoia tiling, Rectangle, Magnet and Moom all share one blind spot: they only know the display setup you built the layout on. Unplug the monitor, or let a dock drop the connection for a second while the Mac sleeps, and macOS has to move your windows off the screen that just vanished. When the monitor comes back, the split is gone and you rebuild it by hand. That is not a bug in any of them, it is outside the job they do. The mechanism is in why your Mac windows move when you unplug a monitor.
Putback is the piece that fills that gap, and it replaces none of the above. It does not create splits or tile anything itself. It watches how your windows are arranged, split screen included, and when the display setup changes it puts every window back exactly where it was in about 0.4 seconds, with a separate memory for each setup you use.
