Here is a thoroughly researched study of Schumann's 246 songs for voice and piano. Eric Sams has written a detailed conspectus of Schumann's songwriting art, its growth and development. For each song, in order of composition, there is a translation, a commentary, and notes on particularly interesting details.
The songs of Robert Schumann bogged me down sometimes and was a pretty slow trudge of a read sometimes! However it was wrapped up beautifully and it was really interesting to see how his life unfolded through his music and the works of literature he used to make his songs. Tragic life but beautiful music and soul. Was very saddening to see how his music reflected his mental decline and subsequent downfall.