There are provided 3,5-disubstituted derivatives of 6,7-dihydroimidazo[1,5-a]pyrazin-8(5H)-one compounds of formula (I) or a pharmaceutically acceptable salt thereof as defined in the present specification, which modulate the activity of protein kinases. The compounds are therefore useful in treating diseases caused by dysregulated protein kinase activity. In particular, such diseases to be treated with a compound of formula (I) of the present invention is one caused by and/or associated with disregulated protein kinase activity selected from the group consisting of cancer, viral infection, prevention of AIDS development in HIV-infected individuals, cell proliferative disorders, autoimmune and neurodegenerative disorders. The present invention also relates to processes for preparing the compounds of formula (I), combinatorial libraries thereof, pharmaceutical compositions comprising them, and methods of treating diseases utilizing pharmaceutical compositions comprising a compound of formula (I).