Modelling as a technique continually keeps important place in information system development (ISD) methodologies and is adopted for implementing systems effectively. Contrasting to modelling, agile methodology is a new concept. It aims to overcome shortcomings of early ISD methodologies. It welcomes changes and adapt to them. Meanwhile it is people-oriented. Used in the new methodologies, besides traditional roles, modelling has more critical roles in ISD methodologies.The report illustrates main roles of modelling, including traditional and new ones. Meanwhile, it also addresses idea of ISD is social with the roles of modelling.