A CDJ is a type of digital music player used by DJs. It was first made to play music from compact discs, but many CDJs can now play digital music files stored on USB flash drives or SD cards. Usually, two CDJs are connected to a DJ mixer. CDJs have special wheels and controls that let DJs adjust the music in ways similar to using vinyl records on turntables. Many CDJs also have features not found on turntables, such as looping, beat analysis, and changing the tempo without affecting the pitch. Some CDJs can also act as controllers to manage music played in software like VirtualDJ and Serato.

Several professional audio companies, including Gemini, Denon DJ, Numark, Stanton, and Vestax, make high-quality CD players for DJs. In 1993, Denon DJ created the first 2-piece rack-mounted dual-deck CD player with a jog wheel and an instant cue button, which became widely used in clubs and by mobile DJs during the 1990s. This design became the industry standard until 2004, when Pioneer introduced the CDJ-1000, which changed the standard. Since then, Pioneer DJ CDJs have been widely considered the industry standard.

Pioneer CDJ models such as the CDJ-400, CDJ-800, CDJ-850K, CDJ-1000, CDJ-900, CDJ-2000, CDJ-3000, and CDJ-3000X include a vinyl emulation mode. This feature lets DJs control music on a CD as if it were on a turntable. Earlier models before the CDJ-1000 did not have this feature. CDJs released after the CDJ-400 can play music from USB sticks and CDs. Pioneer also added its rekordbox software to CDJs, allowing users to prepare music with cue points, accurate BPM, and search/playlist functions.

1990s

The CDJ-500, called the Mark 1 before the second version was released, was introduced by Pioneer DJ as their first CDJ CD player in 1994. A cheaper version, the CDJ-300, was also released in 1994 for those who wanted a less expensive option.

The CDJ-500 was the first Pioneer DJ player to include a Jog Dial, which allowed users to cue CDs, unlike rack-mounted CD players that were common at the time. It had a loop function, loop-out adjust, and other features for looping parts of the music being played. The pitch control could change the speed by +/- 10%, and the Master Tempo feature kept the pitch stable even when the tempo was changed.

All CDJ-500 models had a top-opening CD loading system, which is different from later models like the CDJ-100S (released in 1999), which used front slot-loading for discs.

In later years, Pioneer released the CDJ-500II, which had slightly faster performance, improved Loop Out adjust, and a longer maximum loop time of 10 minutes.

The CDJ-500S, also known as the CDJ-700S in the United States, was released in 1997. It was a smaller version of the CDJ-500 and included an anti-skip system for the first time.

The CDJ-100S was introduced in early 1998. It was a basic CD player with a pitch controller and three sound effect options.

2000s

The CMX-5000, released in March 2000, was Pioneer's first attempt to enter the market for 19" rack mountable dual CD players. Before this, it was possible to install two CDJ-500S players side by side in a standard rack with an optional bracket. This market had been dominated by Denon.

The CMX-5000 had a 2U section with two slot-loading CD drives and a 3U "controller" section with two jog wheels and control buttons for the CD drives below.

The CDJ-1000, later called the MK1 after the MK2 was released, was introduced in 2001. It had "Vinyl Mode," which greatly improved jog wheel performance. This made the CDJ-1000 the first CD player that could closely copy the feel of a vinyl turntable, including the ability to scratch. It quickly became an industry standard for DJs.

The player had a large touch-sensitive platter with a digital display in the center that showed information about the music's position. Unlike a turntable, the platter did not rotate by itself. The display helped DJs cue music accurately. An orange cue marker was also included, similar to stickers used by scratch DJs. A waveform display allowed DJs to see upcoming parts of a track.

The CDJ-1000 and its later versions became widely used in dance clubs and by DJs. It is currently the most common DJ-style CD deck in nightclubs. The player supported playback from CD, CD-R, and CD-RW. It included features like looping, pitch changing, reverse playback, and turntable break-stop and start. It also had the master tempo function, which changed the speed of music without altering the pitch, a feature first introduced on earlier models like the CDJ-500 and CDJ-500S.

Before the CDJ-1000, few clubs used CD decks because they lacked DJ features and were not as durable. Many DJs preferred vinyl because most music was still available on vinyl. The introduction of recordable CD-R and CD-RW discs, along with stand-alone recorders, made it easier for DJs to use the CDJ-1000. Before this, DJs often used expensive acetate discs, which wore out quickly and could not be played after a few uses.

The CDJ-800, released in 2002, had a different jog wheel mechanism. Pressing and releasing the top of the wheel caused it to "quick return." It was designed to offer features similar to the CDJ-1000 at a lower cost for home use. The CDJ-800 had a center detent on its pitch slider, making it easier to center. It did not have the CDJ-1000's "hot cue" feature and could only handle one cue and one loop at a time, though these could be saved for up to 500 CDs. It could change loop "out-points" while playing but not "in-points," requiring loops to be re-captured. Unlike the CDJ-1000, the CDJ-800 could only relay in CDJ jog mode. It also had an "auto-beat" function that the CDJ-1000 did not.

The CDJ-800 was released in November 2002 and stopped being sold in February 2006, when the updated CDJ-800-MK2 was introduced.

The DMP-555 was a single-deck tabletop CD player for DJs, introduced in April 2002 and discontinued in 2004. It had features like playback from SD cards and MP3s from memory cards or optical media. It could cue from one media source and play from another on the same unit, allowing DJs to mix two tracks using only one DMP-555. However, it had limited support, a 2GB SD card limit, and required a special Pioneer-branded writer and custom software to transfer MP3 files due to copyright concerns.

The CMX-3000 was Pioneer's second attempt at a rack-mountable dual CD player. Released in 2003, it was often mistakenly advertised as a

2010s

The CDJ-850 was introduced in 2010 to replace the CDJ-800MK2. It offered improvements over its predecessor and was designed to operate similarly to the CDJ-900 and CDJ-2000. The CDJ-850 was compatible with rekordbox and had an affordable price. However, its tracking accuracy was 1 frame (13ms), which is slower than the CDJ-900's 1ms. This lower accuracy made seamless looping difficult without frequent adjustments. The CDJ-850 also included USB functionality with rekordbox support.

Released in July 2010, the CDJ-850 featured a playlist button, manual and automatic loop options, a vinyl mode for scratching, a tempo adjuster, and a Master Tempo button that changed a song's pitch when disengaged. It could use USB thumb drives and CDs and function as a MIDI controller.

The Pioneer CDJ-2000 was discontinued by the end of 2012 and replaced by the CDJ-2000 Nexus, released in September 2012. The Nexus included a high-resolution screen that displayed detailed waveform information and Beat-Sync, which allowed DJs to automatically match beats from 2, 3, or 4 players using ProDJLink. It was the first CDJ to support playback of music from smartphones or tablets via Wi-Fi or USB.

The CDJ-2000 Nexus was discontinued in early 2016 and replaced by the CDJ-2000NXS2, released in February 2016. In early 2016, Pioneer introduced the CDJ-2000NXS2, which included a high-definition 7-inch touchscreen, eight hot cues, and support for the FLAC file format. It was the first CDJ to support external peripherals like the DDJ-SP1, DDJ-XP1, and DDJ-XP2. The NXS2 allowed instant access to all eight hot cues using an "Add-On" controller. The CDJ-3000, released later, would be the final flagship CDJ model to support Compact Discs, making the NXS2 the last to do so.

2020s

In late 2020, Pioneer released the CDJ-3000. This model does not have a CD drive, unlike earlier CDJ versions. It is similar to Pioneer's XDJ line, such as the XDJ-1000MK2, which also lacks CD drives. The CDJ-3000 includes a larger 9-inch touchscreen, a changed layout with more hot cue buttons (but still has eight hot cues, like the CDJ-2000NXS2), more loop and beat jump buttons, and an LCD screen in the center of the jog wheel.

The CDJ-3000 supports FAT, FAT32, exFAT, and HFS+ file systems. It does not support NTFS or macOS GUID partitioning. FAT or FAT32 is needed when updating the device's firmware.

The CDJ-3000 can stream music from Beatport (using StreamingDirectPlay, which requires a Beatport subscription) and access personal music stored on Dropbox or Google Drive (using CloudDirectPlay, which requires a Rekordbox Cloud Library Sync subscription).

In September 2025, AlphaTheta (previously known as Pioneer DJ) released the CDJ-3000X, an improved version of the CDJ-3000. The CDJ-3000X includes a 10.1-inch touchscreen, built-in Wi-Fi, an NFC touchpoint for connecting to smartphones, new cue functions such as Touch Cue and Gate Cue, and stronger play and cue buttons. The SD card slot was replaced with a USB-C port.