The present invention pertains generally to the field of therapeutic compounds. More specifically the present invention pertains to certain pyridyl-amino-pyrazine carbonitrile compounds that, inter alia, inhibit Checkpoint Kinase 1 (CHK1) kinase function. The present invention also pertains to pharmaceutical compositions comprising such compounds, and the use of such compounds and compositions, both in vitro and in vivo, to inhibit CHK1 kinase function, and in the treatment of diseases and conditions that are mediated by CHK1, that are ameliorated by the inhibition of CHK1 kinase function, etc., including proliferative conditions such as cancer, etc., optionally in combination with another agent, for example, (a) a DNA topoisomerase I or II inhibitor; (b) a DNA damaging agent; (c) an antimetabolite or thymidylate synthase (TS) inhibitor; (d) a microtubule targeted agent; and (e) ionising radiation.