Protein kinase 2 (CK2) is a serine/threonine-selective protein kinase that controls several signaling pathways. The structure of CK2 is tetrameric, which consists of two catalytic and two regulatory subunits. CK2 is a critical regulator of cell cycle progression and it has been observed to regulate cell cycle progression by protein-protein interactions. It is also involved in various biological processes such as DNA damage response, apoptosis, cell proliferation, cell cycle control, circadian rhythm regulation, transcription and translation. Furthermore, other functions of CK2 are related with human infections. There are certain viruses, which exploit the CK2 host cell for sustaining their life. CK2 activity has also been associated with various diseases including cancer, neurological diseases, inflammation, diabetes, obesity, diverse ophthalmic pathologies, and cardiovascular diseases such as cardiac hypertrophy and atherosclerosis. This book aims to shed light on the structure and regulation of protein kinase CK2. It aims to equip students and experts with the advanced topics and upcoming concepts in this area of study.