Your summoned creatures are more powerful and robust.
Prerequisite: Spell Focus (conjuration).
Benefit: Each creature you conjure with any Summon spell gains a +4 enhancement bonus to Strength and Constitution for the duration of the spell that summoned it.
Endzeitgeist Says: If you're playing a summoner, this is a must-have feat - +4 Str and Con are huge benefits that apply to all your minions. If you only rarely summon creatures, choose something else.