The terms paper knife and letter opener are often used interchangeably to refer to a knife-like desktop tool. In truth, they are actually for different functions and were in use at different times.

Paper knives are used for cutting open the pages of hand-produced books where the folding of printed sheets creates some closed edges that require severing of the paper before reading. Letter openers "evolved" from paper knives into longer, blunter blades for the sole purpose of opening envelopes. Paper knives are no longer in common use, except perhaps by antiques enthusiasts.

An electric version of a letter opener is also available, which uses motors to slide the envelopes across a blade, and is also able to handle increased numbers of envelopes, but the blade can slice into the contents of the envelope and damage them.

Letter openers may be designed from wood, metals, such as stainless steel, silver, or pewter, plastic, ivory, or a combination of materials. Often the style of the handle is embellished or styled more so than the blade. Some modern openers have a retractable razor blade inside a plastic handle.