Mesa/Boogie (also known as Mesa Engineering) is a company in Petaluma, California that makes amplifiers for guitars and basses. It has been in operation since 1969. Mesa was started by Randall Smith as a small repair shop which modified Fender combos to give them more gain. Prominent early buyers included Carlos Santana, and Keith Richards of The Rolling Stones, helping to develop Mesa/Boogie's reputation as a major amp builder.

In 1969, Smith, as a joke, modified Barry Melton's Fender Princeton amplifier. He removed the standard 10 inch speaker and modified the chassis to fit the larger transformers that were needed by the 4-10 tweed Fender Bassman, the circuit that he had added into the tiny 12 watt Princeton. Finally, Mounting a 12 inch JBL D-120, a popular speaker of the time, Smith had created what would be the first Boogie.

Randall Smith, needing to test his creation, took the "hot-rodded" Princeton into the front store, where Carlos Santana was present. Santana "wailed through that little amp until people were blocking the sidewalk". Impressed, Santana exclaimed to Smith, "Man, that little thing really boogies!" It was this statement that brought the Boogie name to fruition.

The MESA name came about through Smith's other job, rebuilding Mercedes engines and repairing houses. He needed an 'official' sounding name through which to buy Mercedes parts and building supplies, and chose MESA Engineering. It was originally spelled with all capital letters but has been written as Mesa in recent years.

The Express line introduced Mesa's Duo-Class technology. This technology offers the ability to run the power section of the amplifier in either true class A (single-ended) mode, or true class AB (push-pull) mode. This allows the operator to choose between running the amplifier at a reduced power output of 5 Watts (class A), or full power (class AB). When run in 5 Watt (Class A) mode, the power section is operating on only one vacuum tube.

The 5:25 operates on two EL84 tubes in the power section, and produces a maximum rated power output of 25 Watts. It is available as either a Short Chassis Head (Width 19in), or a 1x10 (Open Back) Combo unit containing one E50 Speaker, and comes with casters included. They also offer a 1x12 (Open Back) Combo unit with one V30 Speaker which offers a bigger sound over the 10" speaker.

Common features among the models in the Express line are as follows:

• Fixed bias current.
• Five 12AX7 tubes.
• Two fully independent channels with four style modes (channel 1 = Clean or Crunch, channel 2 = Blues or Burn).
• independent gain, treble, mid, bass, reverb, master and contour controls per channel.
• Footswitchable Variable Contour Control on each channel, which Mesa Boogie says provides the power of their traditional 5-band graphic EQ from one rotary control.
• All tube, long spring reverb.
• All tube FX Loop external switching Jacks for channel 1/2, contour 1, contour 2, reverb.
• Three button footswitch (Channel 1/2, reverb & contour).