A signal box or signal cabin is a building from which railway signals and points are controlled. Originally all signalling was done by mechanical means; cables or rods, connected at one end to the signals and turnouts and at the other to levers in the signal box, ran alongside the railway. This required signal towers to have complex arrangements of cabling, levers and pulleys. The guts of this system was the lever frame, wherein one finds this complex cabling arrangement and linkage to levers and controls.

Nowadays, some old-style signal cabins can still be found. Some still control mechanical points and signals. More often than not, the frame has now been removed or is out of use. This is due to widespread power signalling. Most modern countries have little, if any, mechanical signalling remaining in the rail system.

The modern control centre has replaced widespread signal cabins. These centres, usually located near main railway stations, control the track network using computer systems. One such system is CTC, Centralised Traffic Control.

In the UK typical modern signal boxes are of the Integrated Electronic Control Centre or IECC, Entrance-Exit panel (NX) or One control switch (OCS) type. Variations of these control systems are throughout the world.