Explore the fundamental concepts of resummation and parton showers in this comprehensive lecture, the first in a series delivered by Emanuele Re at the Galileo Galilei Institute. Delve into the theoretical foundations and practical applications of these crucial techniques in particle physics, gaining insights into their role in understanding high-energy collisions and particle interactions. Over the course of nearly two hours, examine the intricate relationship between resummation methods and parton shower algorithms, laying the groundwork for advanced topics in subsequent lectures.