Imagine the board halfway through a game. Your opponent has built a big framework on one side: stones spaced along the edge, a wall facing inward, a large empty area that is not yet territory but will become territory if nobody enters it. If you leave it alone, you lose. You have to go inside. That is an invasion.
Invading is one of the most frightening moves in Go for newer players. You are placing stones where your opponent is strong, and if the invasion dies, the loss is large. But games are regularly decided by whether one player dares to invade and whether the invasion lives. This article covers the basics: how to judge if there is room, where to land, and what to do once you are inside.
Invasion versus reduction
First, a distinction. There are two ways to deal with a large opposing area:
- Invasion: land deep inside and try to live there, destroying most of the area.
- Reduction: approach from outside, making the area smaller without trying to live inside it.
An invasion wins more if it lives but risks more if it dies. A reduction wins less but is safer. Choosing between them is a matter of counting: if you are behind by a lot, you need the bigger result and must invade. If you are ahead, a reduction may be enough. A separate article covers reduction versus invasion in more depth.
Is there room to live?
Before invading, ask whether there is enough space for a group to make two eyes. Some guidelines that hold on most boards:
- On the third line, a stone needs roughly three or four points of space along the edge on each side to have a realistic chance of making a base.
- The 3-3 point in an empty corner (the point three lines in from both edges) almost always offers a way to live if the corner is not yet closed with extra stones.
- A space between two opposing stones on the third line that is five or six lines wide can often be invaded; narrower gaps are much harder.
- If your opponent has a wall facing the area, the area is harder to invade, because the wall blocks your escape toward the centre.
These are rules of thumb, not guarantees. The only certain test is reading, but the rules of thumb tell you where to look.
Timing: invade early or late?
A common mistake is invading too late. The longer you wait, the more moves your opponent adds to their area, and the harder the invasion becomes. The opposite mistake is invading too early, before the rest of the board is settled, when your opponent can attack your invasion and build profit elsewhere at the same time.
A good moment to invade is when:
- Your opponent's area is clearly the biggest open area on the board.
- Your own groups nearby are safe, so the fight will not create a second weakness for you.
- Your opponent has just played elsewhere, leaving the area thinner than it looks.
Where to land
Where you place the first invading stone matters more than anything that follows. Aim for a point that gives you two possible directions: room to make a base along the edge, and a route to run toward the centre or toward your own stones. An invading stone with two options is hard to kill, because your opponent cannot block both.
Landing on the third line is the usual choice. It makes a base easier than the fourth line and gives more room than the second. In an empty corner, the 3-3 point is a classic invasion because the corner itself helps make eyes.
In this small example, White's stone between Black's lower stones has room on both sides. Black cannot block both extensions at once. That is exactly what a good invasion point looks like.
Once you are inside: live small and fast
After the landing, your only goal is to live. Not to live big, not to capture anything, just to live. Invaders who try to gain extra points inside the area usually die.
- Make a base first. Extend along the edge to create space for eyes.
- Keep an escape route open. If you cannot make eyes, you need to be able to run.
- Do not fight every stone. Answer the moves that threaten your life; ignore those that only reduce your score.
- Accept a small life. A group living with two small eyes inside your opponent's area has already destroyed most of its value.
Light, flexible play is the key. Go players call this sabaki: making shape quickly, being willing to give up a stone or two if that helps the rest live. Heavy play, with many stones in a lump, gives your opponent a clear target.
When the invasion goes wrong
Sometimes you land in the wrong place, or your opponent answers perfectly, and the invasion cannot live. Then you have two options:
- Run toward your own stones or the centre, hoping to connect or make eyes later.
- Sacrifice the invading stones, using the moves your opponent spends capturing them to gain elsewhere.
Sacrifice is a real strategy. If your invasion forces your opponent to spend many moves inside their own area to kill it, you may be able to use the forcing moves you gained to strengthen another part of the board. A dead invasion is not always a lost game.
Defending against an invasion
It helps to think about invasions from the other side too. When your opponent invades your area:
- Attack from the direction that pushes them away from their friends. Do not let them connect out.
- Take away the base. Moves along the edge that remove eye space are often stronger than moves that surround from the outside.
- Do not overplay. If the invader is going to live anyway, make them live small and take profit outside. Trying to kill an invasion that can live often leaves your own stones weak.
Practice
Invasions are learned by doing them. On 9×9 boards, invasions are rarer but still useful practice; on 13×13, they come up in almost every game. Try playing the computer on the home page at 13×13 and deliberately invade its largest area each game. Some invasions will die. That is how you learn where the boundary between "enough room" and "not enough room" lies.
Afterward, sign in on the account page to save and replay your games, and play people on the online page once you feel comfortable. For more on fights after an invasion, see attacking weak groups and capturing races.
Frequently asked questions
How do I know if an area is too small to invade?
Count the space on the third line between the opponent's stones. If there are fewer than about four or five open points and a wall behind, living is usually very hard. When unsure, consider a reduction instead.
Should I invade at the 3-3 point?
In an open corner that has only one opposing stone, the 3-3 invasion is a standard and reliable way to live. In a corner with extra stones around it, read carefully first.
What does "sabaki" mean?
It means playing lightly and flexibly to make a group settle quickly, often giving up a stone or two to keep the rest alive.
Is it bad if my invasion dies?
It is a loss, but not always a disaster. If the moves your opponent spent killing it let you gain elsewhere, you may still be fine.
When should I reduce instead of invading?
When you are ahead, when the area is small, or when your own nearby groups are weak. Reduction takes less risk.
