This paper analyses ministerial expertise of senior ministers and junior ministers (in Dutch: staatssecretarissen) who held office in the Netherlands between 1967 and 2015. Expertise is differentiated between two independent dimensions: technical knowledge with respect to the subject matter of the portfolio, and political knowledge and skills. Results indicate that both types of ministers have considerable political and technical expertise, but junior ministers have relatively and significantly more often technical expertise and senior ministers more often have political expertise. Furthermore, the complete outsider (lacking both technical and political skills) is a rather rare phenomenon in both types of ministers. Besides, although it follows from the watchdog junior minister theory that political expertise is needed to function effectively as a watchdog, there is not a significantly higher frequency of political expertise in the junior ministers when the junior minister and the senior minister are from different parties than when they are from the same party.