The song "Won't You Be My Neighbor?" was written by Fred Rogers in 1967 and was used as the opening theme for each episode of the show.
In the early years of the show, when new episodes were constantly being produced, each show ended with the song "Tomorrow." Starting in 1971, "Tomorrow" was used only on episodes which aired Monday through Thursday, and a new song, called "The Weekend Song" was used on shows that aired on Friday (since he wouldn't be back on the air "tomorrow"). Eventually, the "Tomorrow" song was eliminated entirely, and by 1972 Rogers sang "It's Such a Good Feeling" at the end of every show. Prior to 1972, the original version of "Good Feeling" was used as part of Mister Rogers' general repertoire of songs. When "Good Feeling" became used as a closing theme, it was slightly rewritten, incorporating the first four lines of "The Weekend Song" at the end, though rendered during the week as "And I'll be back when the day is new...", with "day" changed to "week" on Friday episodes.
In 1991, the early episodes were removed from the broadcast circulation and so the "Tomorrow" song hasn't been heard since then. Rogers sang the opening song while entering the set and performing his iconic wardrobe change going from a suit jacket and dress shoes to a more casual cardigan sweater and sneakers, and sang the closing song when he changed back.