Overhead projectors, used in schools, colleges and university classrooms, allow teachers to write ideas down as discussed, which are projected instantly onto a projector screen so that all students can see. OHP's shine light through transparent acetate sheets to display whatever is written or printed on them onto a projector screen. You can also photocopy pages from books onto acetate sheets. Main advantage of an overhead projector (OHP) over a multimedia projector is cost.

Models range from sturdy, budget economy models for prolonged classroom use to stylish, flatbed models for classroom, training and boardroom presentations. Portable flatbed OHP's are available for presentations on the go.

Models on the market also include powerful OHP’s for large audience lecture theatres. Some models have single lamps, whilst others offer twin lamps, which means that should a bulb go in the middle of a presentation, then with a flip of a switch it transfers to the second lamp and your presentation is uninterrupted.