This chapter assesses the varieties, sources, consequences, and challenges of constitutional infidelity in the Nigerian federal system under the 1999 Constitution. Constitutional infidelity in Nigerian federalism is rampant, consequential, and multifaceted. It is rooted in several things, including the dissonance between formal constitutional centralism and the centrifugal dynamics inherent in a multi-ethnic society; the extensive opportunities for informal and unconstitutional behaviour in a neo-patrimonial context; the difficulty of formal constitutional change; and the ambiguities, contradictions, and compromises written into the formal constitutional document. However, constitutional infidelity in Nigeria takes many forms. In particular, it is possible to identify decentralist and centralist forms of constitutional infidelity. The chapter then analyses some of its more benign, decentralist ramifications in an overcentralised political context. Ultimately, the multiple risks, abuses, and challenges associated with constitutional infidelity suggest that it is a problematic and incomplete strategy for the reform, development, and decentralisation of Nigerian federalism.