This is my series of 43 short YouTube videos called Modern Harmony. It is based on a course I taught at the Université de Montréal (in French) for almost 30 years. Now that I am retired I wanted to make it available to a larger public, and in English. It is mainly aimed at composers. The approach is practical, explaining how these harmonic techniques can be used in composition. A few of the core notions come from Persichetti's Twentieth Century Harmony, others are my own. I am especially interested in principles of harmony that apply to more than one style, and also in how various harmonic techniques can be combined seamlessly in the same composition.