Shield

Level: 1

Casting Time: 1 reaction, which you take when you are hit by an attack or targeted by the magic missile spell

Range: Self

Duration: 1 round

An invisible barrier of magical force appears and protects you. Until the start of your next turn, you have a +5 bonus to AC, including against the triggering attack, and you take no damage from  magic missile.

Source: PHB, page 275. Available in the SRD.