When the electric guitar was originally created back in the 1930s, the main intent was simply to create an instrument that could be heard over the increasingly large jazz orchestras. It is highly doubtful that the instrument's inventors could ever have imagined the uses to which their creation would someday be put. The modern electric guitar is a source of an apparently unending array of tones, pitches and sounds. Artists have pushed the instrument's limits in an attempt to find new and innovative noises, and they continue to do so. The sounds of the electric guitar have become an art form in and of them selves, so much so that specific devices have been invented to create them. Such devices are referred to as guitar effects, and they modify the tone, pitch and sound of the electric guitar to help create the sounds that define some modern music genres.

It would be almost impossible to cover the wide range of effects used by electric guitars, so only the most widely used will be covered herein. One group of very popular effects is distortion-related effects. Such effects are produced by distortion pedals, which distort, or "clip" the guitar signal's waveform. Distortion effects fall into four main subcategories: overdrive/distortion, overdrive/crunch, fuzz and hi-gain. Some of these effects are often associated with specific genre or artists. Overdrive/crunch pedals, for example, produce sounds very similar to those in the music of Carlos Santana and Eddie Van Halen. Hi-gain pedals, on the other hand, create the sounds most often connected with the genre of heavy metal.

Then there are the volume-related effects. As with distortion effects, those related to volume are also created via a pedal. The guitarist is able to use this pedal to adjust an instrument's volume during a performance; it can also be used to make a guitar's notes or chords fade in and out. Such attributes are useful during human vocal sections, when the percussive plucking of strings needs to be softened or eliminated altogether. There are at least three different types of volume pedals, these being auto-volume/envelope volume, tremolo and compressor. Each type boasts specific attributes useful to different situations and musical genres.

Time-based effects include delay/echo, looping, and reverberation or "reverb." The first, delay/echo, creates a copy of an incoming sound, delays it slightly and then repeats it either once for a "slap" effect or multiple times for an "echo" effect. Looping involves recording a phrase or passage and then accompanying that passage as it replays. This technique involves the use of extremely long time delays. Finally, reverb refers to the persistence of a sound in a particular space after the original sound is gone. In essence, it is a large and extended number of echoes.

Modulation-related effects include several devices, including the rotary speaker, the rotary speaker simulator, the vibrato pedal, the phase shifter and the flanger. The rotary speaker and its simulator offer something known as a Doppler effect, which is a change in a wave's frequency and wavelength. A vibrato pedal reproduces the sound of the rotary speaker by synchronizing a standard speaker's volume oscillation, frequency-specific volume oscillation, vibrato, phase shifting and chorusing. A phase shifter creates a complex frequency response that results in a "whooshing" noise, similar to that of a flying jet. And finally, if an artist wishes to simulate the sound originally created by slowing a tape down by holding something against the flange and then allowing the tape to speed up again, a flanger can produce such a sound.