This lecture is the first in a series on Coding Theory delivered by Swastik Kopparty as part of the ICTS Workshop on High Dimensional Expanders (HDXs) and Codes. Explore fundamental concepts in error-correcting codes, a field that has been crucial to modern communication systems for over seven decades. The lecture takes place at the International Centre for Theoretical Sciences' Ramanujan Lecture Hall as part of a comprehensive two-week program organized by Irit Dinur, Venkat Guruswami, and Prahladh Harsha. Gain insights into this active research area that has recently experienced significant breakthroughs in list-decodable codes, locally decodable/testable codes, polar codes, and quantum LDPC codes. The workshop brings together researchers from computer science, mathematics, and electrical engineering to explore the intersection between coding theory and high dimensional expansion.