This interactive workshop offers a deep dive into the world of Outside-In Development, guided by the dynamics of Mob Programming. Participants will engage in an exciting fishbowl Mob Programming session, focusing on implementing and designing software from a business-centric perspective. Utilizing tests as a guiding tool rather than a hindrance, the workshop begins with established requirements and acceptance criteria. From there, we will craft an acceptance test that initiates the outer loop of our Acceptance Test Driven Development (ATDD) suite. This test serves as a continuous feedback mechanism, steering the implementation of the feature to completion. Our approach is well-tested and proven in numerous delivery teams, a methodology we have detailed in our award-winning book "Agile Technical Practices Distilled". It incorporates elements of ATDD (London school), Behavior-Driven Development (BDD), classic Test-Driven Development (TDD), Domain-Driven Design, and Modular/Hexagonal Architecture. This technique is exceptionally effective for incrementally expanding system functionality, and ensuring alignment with business objectives. Participants are invited to join the "mob", actively navigating the development process, or to relax and observe the unfolding development journey from the audience. We can deliver the workshop either in Java or C# .NET and we will decide on the spot with a quick poll!