John Kaizan Neptune (born November 13, 1951, in Oakland, California, United States) is an American player and builder of the shakuhachi (Japanese bamboo flute).

In 1973, he continued his shakuhachi studies in Kyoto, Japan, returning after one year to Honolulu to complete a degree in ethnomusicology.

Following his graduation, he traveled again to Kyoto for several more years of intensive study, and in March 1977 he received the "shi-han," or master's certificate, in the Tozan School of Shakuhachi.

Neptune has performed in North America, Europe, Australia, and Asia and recorded more than 20 albums with a variety of musicians.

He also makes shakuhachi and other bamboo instruments at his home workshop in the Japanese countryside.