Phase II evaluation is a critical step in the development of a new treatment, as it provides evidence for go/no-go decision making for further development, as well as information needed for the design of phase III trial. However, in many situations investigators do not have enough information desired for the design of phase II studies due to the lack of previous experience on the primary endpoint of interest, the potential efficacy as measured by the selected endpoint(s), etc. Hence it may limit our ability to make informative decisions for the trial itself and/or even the whole development program. One option is to design and conduct the phase II studies adaptively with some flexibility in terms of sample size re-estimation, and/or dropping treatment arm(s), and so on. The design strategies and their potential applications will be discussed, with examples from oncology, CNS, or other ar