The present invention relates to a ligand and its use in a catalyst for the oligomerization of olefinic monomers, the ligand having the general formula (VI); (R9)(R10)P—N(R3)—P(R4)  (VI) wherein: the R9 and R10 groups are independently selected from optionally substituted alkyl or heteroalkyl groups; the R3 group is selected from hydrogen, a hydrocarbyl group, a substituted hydrocarbyl group, a heterohydrocarbyl group, a substituted heterohydrocarbyl group, a silyl group or derivative thereof; the R4 group is an optionally substituted alkylenedioxy, alkylenedimercapto or alkylenediamino structure which is bound to the phosphorus atom through the two oxygen, sulphur or nitrogen atoms of the alkylenedioxy, alkylenedimercapto or alkylenediamino structure or an optionally substituted arylenedioxy, arylenedimercapto or arylenediamino structure which is bound to the phosphorus atom through the two oxygen, sulphur or nitrogen atoms of the arylenedioxy, arylenedimercapto or arylenediamino structure.