A discussion on the current challenges that face the heat transfer community in predicting two-phase flow patterns in microchannels is presented in this paper. These challenges include lack of universal terminology, a requirement for an agreed flow pattern categorisation by the international research community and subjectivity due to visual categorisations of flow patterns. The generic flow pattern categorisation of bubble, slug, churn and annular flows are suggested to alleviate these problems. Finally, a data bank consisting of over 1500 data points for a range of fluids was used to assess the success of current diabatic flow pattern transition models and to understand the important parameters that cause flow patterns to transition.