The ontological questions ‘What is ICT?’ and ‘What is development?’ are described and documented in literature. Similarly, methodological approaches for understanding how ICT leads to development or for measuring the impact of ICT are described. However, explaining ‘why’ ICT works or not in the contexts of developing countries needs further investigation. We propose a critical realism based methodological approach for answering the above mentioned ‘why’-question. The core of a critical realism based approach is to identify the underlying mechanism(s) that may explain a phenomenon of why ICT leads to development. We demonstrate the proposed methodology through applying it on a case in an ICT4D context from Nepal.