How does China promote its military officers? We present a qualitative study on the determinants (connections versus performance) of the selection of military officers. Drawing on 48 in-depth interviews with serving and retired military officers, we argue that the inability of the rule-based personnel system to assess candidate performance (professional competence and political integrity) leads to the rise of the informal institution of guanxi – a Chinese version of personal connections – in promoting military officers. Guanxi both substitutes for and competes with the formal personnel system. Information received through guanxi networks is used by superiors to evaluate subordinates’ professional competence and political integrity. Guanxi is also used by corrupt officers to distort democratic procedures and facilitate the buying and selling of military positions. We conclude that the co-existence of a rule-based personnel system and guanxi leads superiors to promote competent candidates within their guanxi networks.