Joni Mitchell began her career singing folk songs and writing lyrics that would be performed by musicians like Judy Collins and Fairport Convention. When she began to make albums of her own, her verses became more pointed and her music expanded, growing to incorporate the jazz she had long adored. Even toward the end of her career, Mitchell continued searching for new directions: In 2007, her “One Week Last Summer” won a Grammy for — of all things — Best Instrumental Performance. Here are 10 essential tracks from her half-century of recording.