A catalyst composition suitable for the trimerization of olefinic monomers, wherein the catalyst composition comprises: a) a source of chromium, molybdenum or tungsten; b) a ligand of general formula (I); (R1)(R2)P—X—P(R3)(R4)   (I) wherein: X is a bivalent organic bridging group; R1 and R3 are independently selected from, hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl and substituted heterohydrocarbyl groups, with the proviso that when R1 and R3 are cycloaromatic groups they do not contain a polar substituent at any of the ortho-positions; R2 and R4 are independently selected from optionally substituted cycloaromatic groups, each R2 and R4 bearing a polar substituent on at least one of the ortho-positions; and c) a cocatalyst. The present invention further relates to a process for the trimerization of olefinic monomers, particularly the trimerization of ethylene to 1-hexene, wherein the process comprises contacting at least one olefinic monomer with the catalyst composition described hereinabove.