Countries relatively new to clinical trials such as Asia, Russia, South America, and Eastern Europe are increasingly taking part in global trials. Such multi-regional clinical trials (MRCT) have benefits but also come with a set of challenges. Two of the key challenges are how to define "region” and to assess consistency of treatment effect among such regions. Careful prospective planning taking into account ethnic factors like culture, ethnicity, medical practice, access to competitive therapy and patient/disease characteristic are more important than geography and meaningful in defining region. A good understanding of the relative importance of these factors is crucial in understanding any heterogeneity and treatment consistency in regional populations. Once regions are defined, other challenges include: methods/criteria for assessing consistency of treatment effect among regions, pre-specification and sample size planning at study design stage, and appropriate interpretation/exploration of regional findings. In this talk, points to consider in defining region and consistency assessment from the workstreams of PhRMA Key Issue Team will be discussed.