Thienopyrimidines of formula (Ia) or (Ib): wherein R1-R3 have any of the values described herein, and the pharmaceutically acceptable salt thereof have activity as inhibitors of PI3K and may thus be used to treat diseases and disorders arising from abnormal cell growth, function or behavior associated with PI3 kinase, in particular the p110 delta subtype, such as immune disorders, cardiovascular disease, viral infection, inflammation, metabolism/endocrine disorders and neurological disorders. Processes for synthesizing the compounds are also described.