ESDU ME1 provides an introduction to the use of ESDU 76005, a boxfile of transparent graphs that allows, for the complete range of four-bar planar linkages, the analysis of an existing design to determine its kinematic output or the synthesis of a geometry that achieves a required kinematic output. The method of presentation in which the link lengths are defined in terms of non-dimensional quantities formed from their ratios is explained, and the linkage geometry and types (crank-rocker, slider-crank, parallel-coupler and offset swinging block) for various choices of those parameters illustrated. The data that can be obtained for each geometry include the angle of swing of the rocker, the crank-angle between dead-centres, the rocker angle at extended dead-centre, extreme transmission angle, maximum rocker velocity, maximum crank torque due to rocker inertia and maximum coupler end-load and, for slider-cranks, slider stroke, extension, and maximum slider velocity. In addition to the graphical presentation, analytical expressions are given for all those quantities. Their importance in design is explained and other design considerations such as materials, balancing, forces, vibration, link lengths and backlash are briefly discussed. The force calculations assume zero inertia for the coupler, but representing it by masses placed at the joints with their centre of gravity at the coupler centre of gravity is considered and equations are provided to adjust the results using that idealisation or using the true inertia. Worked examples show how the transparencies are used to select the link lengths to achieve a required design and to optimise it.