Queen's Gambit Declined Slav - 4.e3 Bf5

White moves the queen's pawn to d4. Black plays the queen's pawn to d5. White plays the c-pawn to c4.

Black moves the c-pawn to c6. White develops the knight to f3. Black develops the knight to f6.

White pushes the king's pawn to e3. Black develops the light-squared bishop to f5.