A series of pyrazolo[3,4-b]pyridine derivatives that are substituted at the 4-position by a diaza monocyclic, bridged bicyclic or spirocyclic moiety, being selective inhibitors of phosphatidylinositol-4-kinase IIIβ (PI4KIIIβ) activity, are beneficial in the treatment and/or prevention of various human ailments, including inflammatory, autoimmune and oncological disorders; viral diseases and malaria; and organ and cell transplant rejection.