Informal institutions, or conventions or codes of behaviour, play significant role in constraining human behaviour that have important political consequences. Despite a lot of focus on institutionalism, informal institutions\u27 role in political behaviours and outcomes has not been scrutinized thoroughly in political science. This paper investigates the contribution of informal institutions to the political exclusion of marginalized groups like Dalit, indigenous nationalities, Madhesi, and women in democratic Nepal (1990-2002). Scholars have pointed out the role of formal institutions like the unitary state, first past the post electoral method in the exclusion in Nepal. However, formal institutions do not account for all the exclusion. Not a single Dalit was nominated to the cabinet during 1990-2002. This was not due to formal restriction but because of informal norms like caste system that guide political and social actors’ behaviours. In this paper I will discuss various ways informal institutions interacted with formal institutions during the democratic years to produce exclusion. Specifically, I will analyze the role of patriarchy on the exclusion of women, hill nationalism and the exclusion of Madhesi, and caste system and Bahunbad and the exclusion of indigenous nationalities and Dalit. Analyses of informal institution are important because even if formal institutions are changed, exclusion may still continue because informal institutions persist for long periods
