Rule of law promotion and security sector reform (SSR) are expected to abide by the same guiding principles. Actors involved in both endeavors are demanded to base their activities on a solid knowledge base. They are urged to take a holistic approach and to ensure that particular components of such an approach are properly coordinated. They are pushed to strive towards local ownership. And, the credibility of external actors is deemed to be of paramount importance. However, there is wide consensus that both rule of law promotion and SSR by and large fail to adhere to these guiding principles. SSR practitioners would thus be ill-advised to rely on applying best practices from rule of law promotion, the older and more established field, to their own endeavor. Rather, both fields ought to step up their efforts to develop practically relevant lessons learned that could then, in turn, be reciprocally useful.