Open D Tuning is a guitar tuning that allows the strings to create a D major chord when strummed without pressing any frets. In this tuning, the strings are adjusted to the notes D-A-D-F#-A-D, from the lowest to the highest string. This setup is popular among guitarists for its rich, resonant sound and ease of playing chords. Many musicians, including Robert Johnson and Derek Trucks, have utilized Open D Tuning to achieve unique musical expressions. It is particularly favored in genres like blues and slide guitar playing, as it facilitates smooth transitions and vibrant harmonics.