Captured pieces are truly captured in shogi. They are retained "in hand", and can be brought back into play under the capturing player's control. On any turn, instead of moving a piece on the board, a player may take a piece that had been previously captured and place it, unpromoted side up, on any empty square, facing the opposing side. The piece is now part of the forces controlled by that player. This is termed dropping the piece, or just a drop.

A drop cannot capture a piece, nor does dropping within the promotion zone result in immediate promotion. However, either capture or promotion may occur normally on subsequent moves by the piece.

A pawn, knight, or lance may not be dropped on the far rank, since it would have no legal move on subsequent turns. Similarly, a knight may not be dropped on the penultimate rank.

There are two other restrictions when dropping pawns:

A pawn cannot be dropped onto the same file (column) as another unpromoted pawn controlled by the same player. (A tokin does not count as a pawn.) A player who has an unpromoted pawn on every file is therefore unable to drop a pawn anywhere. For this reason it is common to sacrifice a pawn in order to gain flexibility for drops.
A pawn cannot be dropped to give an immediate checkmate. However, other pieces may be dropped to give immediate checkmate, a pawn that is already on the board may be advanced to give checkmate, and a pawn may be dropped so that either it or another piece can give checkmate on a subsequent turn.
It is common for players to swap bishops, which face each other across the board. This leaves each player with a bishop "in hand" to be dropped later, and gives an advantage to the player with the stronger defensive position.