If you wish to understand the Summoner class and to expand the options available to these magical masters, the Summoner’s Circle is an excellent sourcebook. Summoners and conjurers will especially benefit from the feats but others will too.
The Summoner’s Circle: Advanced Feats is a 19-page PDF (17-pages if you remove the cover, ad and OGL page) for the Pathfinder RPG written by Sigfried Trent and published by Open Design. This is part of Open Design’s Advance Feats line for Pathfinder.
Sea of Stars RPG Design Journal 