In industrialized countries, a hammer drill is usually a handheld power drill (tool), which, in addition to the usual rotary mode, has additional drilling modes in which the drill bit either is given both a rotary and a linear motion, or a linear motion (i.e., "hammer") alone. The linear action helps drill in hard materials such as stone and concrete. There are also hand-operated hammer drill bits, which also are used to make holes in hard material.
The hammer drill is very similar to a rotary hammer, and the difference, in some cases, is no more than the manufacturer's product designation. A rotary hammer tends to be a more powerful tool, and may or may not have a rotary-only function. Rotary hammers also may have other features that lend them to heavier work.
To select the linear (hammer) or combined (hammer-drill) mode on most commercial drills, the user pulls back on a spring-loaded collar mounted behind the drill chuck, rotates it to a position for the desired mode, and releases it. This will select appropriate drive mechanisms inside the body of the tool.
While a hammer drill might seem the most versatile type, it generally is less precise than a rotary-only drill, and may not be the best choice for an occasional home user. In like manner, rotary hammers may be more appropriate for the frequent user.