The prevalent affirmative action policy in school choice limits the number of admitted majority students to give minority students higher chances to attend their desired schools. There have been numerous efforts to reconcile affirmative action policies with celebrated matching mechanisms such as...

This thesis consists of three chapters. In the first chapter, we consider coalition formationgames with externalities. A natural extension of superadditivity is not sufficient to imply that the grand coalition is efficient when externalities are present. We provide a condition, analogous to...

We introduce a new mechanism for call auctions which are widely used in stock exchanges. By incorporating contingent claims (buy stock A, if selling stock B) into the price discovery process, we achieve a higher liquidity in call auctions and lower volatility after opening call auctions. We also...