Naturalness string landscape and multiverse : a modern introduction with exercises Reminder of SM EFTs and a naive view of the hierarchy and cosmological constant problems Basics of SUSY and SUGRA A crash course on strings and how to derive the 10d supergravity action for Type IIB Kaluza Klein compactifications Calabi Yau compactifications Flux landscape in a toy model Flux landscape in Calabi Yaus Moduli stabilization and uplift Landscape statistics Eternal inflation The Measure Problem. This book presents a string theoretic approach to new ideas in particle physics also known as Physics Beyond the Standard Model and to cosmology. The concept of Naturalness and its apparent violation by the low electroweak scale and the small cosmological constant is emphasized. It is shown that string theory through its multitude of solutions known as the landscape offers a partial resolution to these naturalness problems as well as suggesting more speculative possibilities like that of a multiverse. The book is based on a one semester course as such it has a pedagogical approach is self contained and includes many exercises with solutions. Notably the basics of string theory are introduced as part of the lectures. These notes are aimed at graduate students with a solid background in quantum field theory as well as at young researchers from theoretical particle physics to mathematical physics. This text also benefits students who are in the process of studying string theory at a deeper level. In this case the volume serves as additional reading beyond a formal string theory course.