This realist review explored causal pathways of the possible consumer effects of health sector demand-side financial (DSF) incentives, their contextual factors and mechanisms in low-and-middle-income countries. We searched six electronic data bases and identified 659 abstracts with different evaluation designs. Based on methodological rigor and content relevance, only 24 studies published up to April 2013 were selected for the final review. A conceptual framework consisting of various program theories on potential context-mechanism-outcome (C-M-O) configuration of DSF initiative was designed, tested and adapted during the review. Synthesized results were presented as a C-M-O configuration for each of the consumer -side effect. DSF was effective to improve health seeking behaviour considerably and health status to some extent. The causal pathway of DSF's functioning and effectiveness was not linear. Key demand-side contextual factors which affected DSF's consumer-side effects were background characteristics of the beneficiaries including their socio-cultural beliefs, motivations, and level of health awareness. At the supply-side, service availability status and provider incentives were contextual determinants. The mechanisms which enabled the interaction of contextual influence were consumer and provider accountability and consumer trust on providers. In order to enhance DSF programs' effectiveness, their design and implementation should carefully consider the potential contextual elements that may influence the causal pathways. Significance for public healthThis article focuses on a rare topic i.e. Realist Review, which is an emerging concept to explore causal factors behind every intervention that make it effective or ineffective. This manuscript is a first attempt on a Realist Review of health sector demand-side financing (DSF) in a number of low-and middle-income countries. DSF is a widely employed health promotion strategy in many countries to improve health seeking behaviour. However, the existing evidence explores only its effectiveness and not the determinants of its effectiveness. It is also essential to understand the causal pathways of DSF's effectiveness, i.e. what are the factors affecting its effectiveness. This Realist Review attempts to explore the causal pathways of effectiveness of many prominent DSF initiatives in the world. The study findings have policy implications and will be widely referred to in future.