The search for efficient group sequential and adaptive designs poses interesting challenges.It is essential to control the type I error rate, or the familywise error rate when multiple hypotheses may be tested. Thus, efficient trial designs should have good properties over a range of possible scenarios while meeting complex requirements on type I error and possibly on power too. I shall illustrate how frequentist and Bayes methods can be combined to find efficient solutions to clinical trial designs. The talk will focus on early stopping through the use of group sequential tests, and sample size modification. I shall briefly discuss related issues in seamless Phase 2-3 trials and adaptive enrichment designs.