A scissor lift is a type of aerial work platform that can usually only move vertically, usually with common working height ranging from 6 meter to 18 meter. The mechanism to achieve this is the use of linked, folding supports in a criss-cross X pattern, known as a pantograph (or scissor mechanism). The upward motion is achieved by the application of pressure to the outside of the lowest set of supports, elongating the crossing pattern, and propelling the work platform vertically. The platform may also have an extending deck to allow closer access to the work area, because of the inherent limits of vertical-only movement.
These units are able to drive themselves (on wheels or tracks) around a site (they usually require to be transported to a site, for reasons of safety and economy). In some instances, these units will be able to move whilst the job is in progress, although this is not possible on units which require secure outriggers, and therefore most common on the scissor lift types. The power can be almost any form of standard mechanical drive system, including electric or gasoline powered, or in some cases, a hybrid (especially where it may be used both inside and outside).
The contraction of the scissor action can be hydraulic, pneumatic or mechanical. Depending on the power system employed on the lift, it may require no power to enter  “descent” mode, but rather a simple release of hydraulic or pneumatic pressure. This is the main reason that these methods of powering the lifts are preferred, as it allows a fail-safe option of returning the platform to the ground by release of a manual valve.
Apart from the height and width variables, there are a few considerations required when choosing a scissor lift. Electric scissor lifts have smaller tyres and can be charged by a standard power point. These machines usually suit level ground surfaces and have zero or minimal fuel emissions and mostly indoor works. Diesel scissor lifts have larger rough terrain tyres with high ground clearance for uneven outdoor surface conditions. Many machines contain outriggers  that can be deployed to stabilise the machine for operation.