This library enables you to communicate with USB devices from userspace. It is implemented as a high-level wrapper around bindings-libusb (http://hackage.haskell.org/package/bindings-libusb) which is a low-level binding to the C library: libusb-1.* (http://libusb.org/). The USB transfer functions in this library have a simple synchronous interface (they block) but are implemented using the libusb asynchronous interface. They integrate with the GHC event manager making them efficient (no busy-loops) and interruptible (throwing an exception to the thread executing a transfer immediately cancels the transfer). If the GHC event manager is not available (because you're either not using GHC or because you're on Windows) the library degrades gracefully to the libusb synchronous implementation. This documentation assumes knowledge of how to operate USB devices from a software standpoint (descriptors, configurations, interfaces, endpoints, control/bulk/interrupt/isochronous transfers, etc). Full information can be found in the USB 2.0 specification (http://www.usb.org/developers/docs/). For an example how to use this library see the usb-example package (https://github.com/basvandijk/usb-example) or the ls-usb package (http://hackage.haskell.org/package/ls-usb). Besides this API documentation the following sources might be interesting: The libusb 1.0 documentation (http://libusb.sourceforge.net/api-1.0/). The USB 2.0 specification (http://www.usb.org/developers/docs/). The bindings-libusb documentation (http://hackage.haskell.org/package/bindings-libusb). "USB in a NutShell" (http://www.beyondlogic.org/usbnutshell/usb1.htm).