This article focuses on the six pieces for orchestra, the earliest from 1998 and the most recent from 2011, by the American composer and filmmaker Phill Niblock (b.1933). These works stand apart from Niblock's more usual practice: that of making compositions on tape (later on computer) by superimposing layers of recordings of held tones played by individual instruments, the tones pitch-shifted to make dense, microtonal drone textures. Yet there are many similarities, in intent if not in sounding result. The article examines the manner of construction of the orchestral works, with emphasis on their pitch structure, and describes the performance practice that has grown around them in recent years. It describes Niblock's particular use of microtonal intervals (approximated in his notation in increments of a sixteenth of a tone) in generating both the textures and the overall form of his compositions, as well as the intended spatial distribution of the musicians in several of the pieces.