In Plasmodium, calcium-dependent protein kinase 4 (CDPK4) is essential for the process of male gametogenesis, where eight flagellated male gametes are produced from a single male gametocyte in ten minutes. This thesis characterised the molecular roles of CDPK4 during male gametogenesis and identified substrates of CDPK4 which mediate the respective molecular processes. CDPK4 mediates the initiation of DNA replication and promotes mitotic spindle formation through SOC1 and SOC2, and initiates axoneme motility through SOC3. A subsequent study uncovered a functional interaction network involving CDPK4, the cGMP-dependent protein kinase (PKG) and another CDPK of the same family, CDPK1, persevered in multiple life cycle stages. Upstream PKG mobilises intracellular calcium and subsequently activates CDPK4 and CDPK1, which mediate erythrocyte invasion and parasite motility in the mosquito gut. A substrate of CDPK4, SOC6 which mediates the aforementioned processes is equally involved in erythrocytic and mosquito stages.