Methods of inhibiting phosphatidylinositol 3-kinase delta isoform (PI3K) activity, and methods of treating diseases, such as disorders of immunity and inflammation, in which PI3K plays a role in leukocyte function are disclosed. Preferably, the methods employ active agents that selectively inhibit PI3K, while not significantly inhibiting activity of other PI3K isoforms. Compounds are provided that inhibit PI3K activity, including compounds that selectively inhibit PI3K activity. Methods of using PI3K inhibitory compounds to inhibit cancer cell growth or proliferation are also provided. Accordingly, the invention provides methods of using PI3K inhibitory compounds to inhibit PI3K-mediated processes in vitro and in vivo.