Two persons play a game on a board divided into $3\times 100$ squares. They move in turn: the first places tiles of size $1\times2$ lengthwise (along the long axis of the board), the second, in the perpendicular direction. The loser is the one who cannot make a move. Which of the players can always win (no matter how his opponent plays), and what is the winning strategy?
1. **Initial Setup and Strategy**:
   - The board is divided into $3 \times 100$ squares.
   - The first player places $1 \times 2$ tiles lengthwise (along the long axis of the board).
   - The second player places $1 \times 2$ tiles perpendicular to the first player.
   - The goal is to force the opponent into a position where they cannot make a move.

2. **Central Row Strategy**:
   - The first player focuses on the central row, which we will call row X.
   - The first player places $1 \times 2$ tiles horizontally on row X.

3. **Effect of the Second Player's Moves**:
   - When the second player places a tile, it will occupy one cell of row X and one cell of either the first or third row.
   - This means that the number of remaining cells in row X decreases by 1 for each tile placed by the second player.

4. **Counting Remaining Cells in Row X**:
   - Initially, row X has 100 cells.
   - After the first player's move, there are 98 cells left in row X.
   - After the second player's move, there are 97 cells left in row X.
   - This pattern continues, reducing the number of cells in row X by 1 after each of the second player's moves.

5. **First Player's Moves**:
   - The first player continues placing tiles horizontally on row X until there is only 1 cell left in row X.
   - This means the first player places 33 tiles (each covering 2 cells) on row X, reducing the number of cells from 100 to 34.

6. **Final Moves**:
   - The first player then places tiles on the first or third row corresponding to the 33 tiles placed on row X.
   - The second player places a tile, reducing the number of cells in row X to 0.
   - The first player continues placing tiles on the first or third row corresponding to the 33 tiles placed on row X.

7. **Endgame**:
   - The second player will eventually run out of moves because they cannot place a tile without overlapping an already occupied cell.
   - Therefore, the first player wins.

\[
\boxed{\text{First player wins}}
\]