4Bb5

4Bb5 is a chess notation symbol indicating White’s fourth move in a game, namely moving a bishop to b5. The move is most commonly encountered in the Four Knights Game, a versatile opening that arises after the sequence 1 e4 e5 2 Nf3 Nc6 3 Nc3 Nf6, with White often playing 4 Bb5 as a developing and potentially disruptive choice.

In the Four Knights Game, 4 Bb5 places the light-squared bishop on the long diagonal toward the center and queen side. From f1, the bishop can reach b5 along the path f1-e2-d3-c4-b5, a maneuver aimed at increasing piece activity, applying pressure on the c6 knight, and influencing Black’s central and queenside development. While the diagonal b5–e8 is not immediately a pin because the d7-pawn often blocks the line to the king, the move b5-bishop pressurizes Black’s knight on c6 and contributes to White’s flexible plan in these lines.

Common Black responses to 4 Bb5 include 4...d5, challenging White's center and opening lines for counterplay, or 4...d6, continuing development while keeping options open for …e5 or …Be7. Other continuations are possible, depending on Black’s chosen pawn structure and piece development. The move 4 Bb5 can lead into a variety of transpositions, and its effectiveness depends on subsequent play, including how White responds to Black’s central breaks and piece maneuvers.

Overall, 4 Bb5 is a standard, flexible option within the Four Knights framework, valued for active piece play and the potential to steer the game into less common, strategic lines.