An open mic or open mike (shortened from "open microphone") is a live show at a venue such as a coffeehouse, nightclub, comedy club, strip club, or pub, often taking place at night (an open mic night), in which audience members may perform on stage whether they are amateurs or professionals, often for the first time or to promote an upcoming performance. As the name suggests, performers are usually provided with a microphone plugged into a PA system so that they can be better heard by the audience.

Performers may sign up in advance for a time slot with the host, who is typically an experienced performer or the venue's manager or owner. The host may screen potential candidates for suitability for the venue and give them a time to perform during the show. Open mics are focused on performance arts such as comedy (whether it be sketch or stand-up), music (often acoustic singer-songwriters), poetry, and spoken word. It is less common for groups such as rock bands or comedy troupes to perform, mostly because of the space and logistical requirements of preparing equipment and soundchecking such groups.

Open mics may have very low entrance fees or no entrance fees at all, although the venue itself may prepare a gratuity jar, a "pass the hat" for donations, or a raffle with various prizes. Venues that charge no fees profit from selling drinks and food. The performers are not typically paid, although the venue may give them food or drink. If the host is an experienced professional and not the owner or the manager of the venue, they are usually paid for their services and may perform at some point during the evening, either preparing a full performance of their own or filling in at short notice when a performer is unavailable. Open mics are somewhat related to jam sessions, in that they both see amateur performers being given the opportunity to perform. The difference is that jam sessions often involve musical ensembles, possibly even a house band or rhythm section, and may involve the participation of professional performers.

Open mics provide an opportunity for emerging musicians to gain experience performing to a live audience without having to go through the process of getting normal music gigs, which is very difficult to do without experience or a demo recording.^{[citation needed]} They provide an outlet for singer-songwriters. Prior to their popularity, the only outlets generally were folk clubs, which were not always friendly towards creators of new music and preferred traditional popular music. They also suggested that music performed by acoustic musicians or solo artists in this manner would necessarily be folk music, a misconception that still commonly exists today. Some organizers have chosen the title "acoustic night" or "acoustic club" in an attempt to indicate an event run broadly on the lines of a folk club, but with a much wider range of musical styles.^{[citation needed]}

Open mic events are most commonly held in the middle of the week or at the very end of the weekend when footfall through venues is low. They rarely occur on the hallowed Friday and Saturday night time slots, when venues are busy with weekend customers and any live performances are professionals who have been booked. The most common night for an open mic in the United Kingdom is Thursday, with Wednesday in second place.

A popular open mic arrangement in the United States is the "Blues Night". In this format, a bar or club will dedicate a particular night, usually in the middle of the week, as being "open mic blues night". The establishment may supply a house band, typically guitar, bass, and drums, and sometimes a keyboard. Singers, guitarists, and harmonica performers who wish to play sign up, usually with the host. This person is tasked with screening the performers, choosing and ordering, and getting the performers on and off stage in a polite manner.

Since the songs chosen need to be simple enough so that a band of musicians who have not played together can perform them without practice, blues standards are used. Songs might be announced as a "12-bar fast shuffle in C" or "slow 12-bar blues in F", or similar phrases that should be familiar to all concerned. Lead singers, keyboards, horn players (usually saxophones), and various percussion instruments are common additions.

Stand-up comedy open mic nights can be held at established comedy clubs but are more commonly held at other venues with or without a stage, often the upstairs or back room of a pub or bar, or at a bookstore, college campus, rock club, or coffeehouse. Less commonly, they are also held at venues such as strip clubs and comic book shops. Comedy clubs may be the only open mic establishments that have a green room, a backstage area for performers waiting to go on stage where no audience members are present.