Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. Bc4/3...Bc5/4. O-O

=Giuoco Piano=

4. O-O
White chooses a quiet path, that tends to transpose to the Giuoco Pianissimo after white plays 5. d3.

Theory table
'''1. e4 e5 2. Nf3 Nc6 3. Bc4 Bc5 4. O-O'''