This article critically evaluates existing causal explanations for the persistence of informality in artisanal and small-scale mining (ASM). These explanations share a legalistic focus on entry barriers and political impediments that prevent or discourage the formalization of poverty-driven ASM operators: however, they fail to fully explain cases such as that of the Philippines, where ASM is characterized by differentiation between a poverty-driven workforce and a dominant stratum of ASM entrepreneurs. Even where limited formalization frameworks provide ASM with a degree of legal recognition, this recognition is usually restricted to these more powerful ASM interests, while excluding the workforce at large. This article therefore proposes an integrative approach to analysing informality in ASM, which complements the existing legalistic focus on entry barriers with a structuralist concern over the exploitation of informal labour. Seen from this perspective, the massive expansion of ASM in the Philippines can be seen as the product of a transition away from capital-intensive large-scale mining to a flexible regime of accumulation built around the exploitation of informal ASM labour. This observation highlights the need to pay more critical attention to the economic logic and the vested interests underlying the (selective) persistence of informality in the workforce.