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The Ruger rimfire semiautomatic pistols are some of the most popular handguns made, with over 3 million sold. They are manufactured by Sturm, Ruger & Company.

The most prevalent model is the MK II, pronounced "Mark Two", made from 1982 to 2005. Previous models include the Standard, Ruger's first model, made from 1949 to 1982, and the MK I Target, made from 1951 to 1982. Variations include the Target models, which have heavier barrels and adjustable sights, and the 22/45 models, which have a polymer frame with a grip-angle that matches the Colt 1911 rather than the steel frame's Luger P08-like layout. The MK II was removed from production in 2004, when it was replaced by the MK III. All Ruger rimfire pistols are chambered in .22 Long Rifle only.

Ruger Standard pistol, with aftermarket adjustable sights, made in 1963

The original Ruger pistol, now called the Standard, had no model number, as it was the first, and for a time only, gun made by Sturm, Ruger. It had a 4.75" lightweight barrel, and fixed sights. The MK I added a Target model, which had a 5.5" bull barrel, or a 7" heavy taper barrel and adjustable sights. The MK II added a slide stop that held the slide open on the last round, and also was available in stainless steel. The MK II has been available in a number of barrel lengths; 4.75" and 6" lightweight barrels; 4", 5.5", 6.875" and 10" bull barrels, and 5.25" and 6.875" heavy tapered barrels. All guns with bull or heavy tapered barrels are Target models, and are equipped with target sights consisting of an adjustable rear sight and a taller, wider front sight, with an aggressive undercut to reduce glare.

Some special variants that command higher prices are the Government Model, a model that was used for pistol training and competition by the US Army, and the Red Eagle models, which were made from 1949 to the year of company co-founder Alexander Sturm's death, in 1952. The Red Eagle models had the Ruger logo in red on a silver background. Since then, the Ruger logo on the grip panels has been either black on silver or silver on black, with the exception of a special 50th Anniversary model that had a silver eagle on a red background. The top of the line Government Competition Model comes with a 6.875" "slab side" barrel (a bull barrel with the sides milled flat to save weight), laminated wood thumbrest grips, a low profile scope base, and scope rings; with the addition of a pistol scope, it makes an ideal entry level bullseye pistol.

The MK II has also been used extensively by the US Navy Seals, in a specially-made integrally-silenced version. See List of individual weapons of the U.S. Armed Forces

Disassembly of these pistols is accomplished with the removal of a mainspring housing/bolt stop pin assembly and can be done very quickly. Re-assembly can be tricky however as the gun must be tilted so the barrel is 135 degrees from horizontal as the mainspring housing is latched in place (final step of assembly). If this is not done, then the hammer strut will not properly seat, and the hammer will not be able to move backwards. This is immediately obvious by the fact that the bolt can only be moved back a fraction of an inch (a few millimeters). By tilting the gun so the hammer strut lies in the correct position as the mainspring housing is closed, the strut is guided into place in the cup on top of the mainspring, and it locks into place when the mainspring housing is latched.

• Instruction Manual - Ruger's instruction manual.
• Parts Booklet - Ruger's official parts list and exploded assembly diagram.
• Field Stripping - guide to field stripping the pistol, with images.
• Assembly/Disassembly - guide to full assembly/disassembly.
• Overtravel - How to adjust the overtravel screw on a Ruger MK II Target model.