Espresso or caffè espresso is a concentrated coffee beverage brewed by forcing very hot, but not boiling, water under high pressure through coffee that has been ground to a consistency that is between extremely fine and powder. Invented by Edward Loysel de Santais in 1843, Santais's machine impressed visitors to the Paris Exposition of 1855 by producing "two thousand cups of coffee an hour." Santais's machine brewed coffee a pot at a time; however, and used steam pressure, though not to force the brewing water directly through the coffee. Instead, it raised the water to a considerable height above the coffee. From there it descended through an elaborate system of tubes to the coffee bed. The weight of the hot water, not the trapped steam, applied the brewing pressure.

Espresso was developed in Milan, Italy in the early 20th century, but up until the mid-1940s it was a beverage produced solely with steam pressure. The invention of the spring piston lever machine and its subsequent commercial success changed espresso into the beverage we know today. Espresso is now produced with between 9 and 10 atmospheres or bars of pressure.

The defining characteristics of espresso include a thicker consistency than drip coffee, a higher amount of dissolved solids than drip coffee per relative volume, and a serving size that is usually measured in shots, which is about 30ml (1 ounces) in size. Espresso is chemically complex and volatile, with many of its chemical components quickly degrading from oxidation or loss of temperature. Properly brewed espresso has three major parts: the heart, body, and the most distinguishing factor, the presence of crema, a reddish-brown foam that floats on the surface of the espresso. It is composed of vegetable oils, proteins and sugars. Crema has elements of both emulsion and foam colloid.

As a result of the high-pressure brewing process, all of the flavors and chemicals in a typical cup of coffee are concentrated. Because of its intense and high concentration of ingredients (including caffeine), espresso lends itself to mixing into other coffee based drinks, such as lattes, cappuccini, macchiati and mochas, without being diluted in the resulting drink. Espresso contains approximately twice the caffeine content per volume as regular brewed coffee, at approximately 40 milligrams per fluid ounce, but only about 1/3 the content per serving.

Preparation of espresso requires an espresso machine, as it is the process that makes espresso the beverage that it is. The act of producing a shot of espresso is termed "pulling" a shot. The term derives from lever espresso machines, which require pulling down a handle attached to a spring-loaded piston, forcing hot water through the coffee at the requisite pressure. To pull a shot of espresso, a metal filter-basket is filled with 7 to 10 grams of ground coffee for a single shot or 12 to 18 grams for a double shot. The espresso is then tamped into a firm puck of coffee. The portafilter (or group handle) holds the filter-basket and is locked under the grouphead's diffusion block. When the brew process begins, pressurized water at 90±5 °C (200±9 °F) and approximately 900 kPa (130 PSI) is forced into the grouphead and through the ground coffee in the portafilter. Water cooler than the ideal zone causes sourness; hotter than the ideal zone causes bitterness. High-quality espresso machines control the temperature of the brew water within a few degrees of the ideal. The serving temperature of espresso is significantly lower, typically around 60-70 °C, owing to the small serving size and the cooling effects of the cup and the pouring process.

This process produces a rich, almost syrupy beverage by extracting and emulsifying the oils in the ground coffee. An ideal shot of espresso should take between 17 and 26 seconds to arrive on a professional-grade machine (optimum at 22 seconds), timed from when the machine's pump is first turned on (unless the machine has a "preinfusion" stage, which may add about 7 seconds to the process). Varying the fineness of the grind, the amount of pressure used to tamp the grinds, or the pump pressure itself can be used to bring the extraction time into this ideal zone. Most prefer to pull espresso shots directly right into a pre-heated demitasse or shot glass, to maintain the ideal temperature of the espresso and preserve all of its crema. Apart from the espresso made manually by a barista, most espresso is made by automatic machines in which the brewing process takes place with an espresso-brewer.

Freshly brewed espresso must be served or mixed into other coffee beverages immediately, or it will begin to degrade due to cooling and oxidation. Temperature and time of consumption are important variables that must be observed to enjoy an ideal espresso; it should be consumed within 2 minutes from when it is served.

A recent North American brewing trend came with the introduction of the bottomless portafilter, that is, a portafilter without the bottom half, exposing the basket and causing the espresso to bypass contact with the portafilter during extraction. The bottomless portafilter serves as a tool to analyze evenness of grind distribution and tamping, as a greater volume of espresso will flow from low-density areas of the coffee puck. Some prefer the taste, citing the portafilter's capacity to preserve crema. Crema is also known as Schuma in South America.