Apicomplexans are obligate intracellular parasites that evolved from a common ancestor hundreds of millions of years ago that also gave rise to ciliates, dinoflagellates, and the relatively recently discovered group of alga commonly referred to as 'chromerids'. Arguably,apicomplexans represent the world’s most successful and diverse parasitic lineage with a global impact on human health, food security and economics. Malaria-causing Plasmodium species, Toxoplasma and Cryptosporidium are amongst the worst known parasites of mankind. Parasites such as Neospora, Theileria, Babesia and Eimeria are important threat to global food security. To understand how a parasitic life style has originated and diversified inapicomplexans, we are engaged in sequencing and comparative genome analysis of a large number of apicomplexans and photosynthetic chromerids, the closest known photosynthetic relatives of apicomplexans. We are also engaged in studying host-parasite interactions in apicomplexan parasites using functional genomics approaches.