The present invention relates to 3-amino-pyrazolo[3,4-d]pyrimidin-4-ones particularly useful as cyclin dependent kinase (CDK) inhibitors, pharmaceutical compositions comprising the same and the use thereof in particular in the prophylaxis and/or treatment of cancer and other proliferative diseases. Furthermore the present invention relates to processes for the synthesis of said 3-amino-pyrazolo[3,4d]pyrimidin-4-ones and intermediates to be used in the processes of the present invention.