permissions problems when using libusb

["Britton Kerin" <bkerin@fastmail.fm>]

I have a program that uses libusb and it only works from root.  When I
try
to run as a normal user I get errors like this:

avrdude: usb_open(): cannot read serial number "error sending control
message: Operation not permitted"
avrdude: usb_open(): cannot read product name "error sending control
message: Operation not permitted"
avrdude: usbdev_open(): error setting configuration 1: could not set
config 1: Operation not permitted

I didn't see a usb group in /etc/group or anything like that.  Can
anyone
tell me the preferred way to let users run programs that use libusb?

Thanks,
Britton Kerin