They were formed as Dinosaur in 1983 in Amherst, Massachusetts by J Mascis (guitar and vocals) and his high school classmate Lou Barlow (bass guitar), following the break-up of their hardcore punk band Deep Wound. Shortly afterwards, Murph (Emmett Patrick Murphy, drums) joined them. Their debut album, Dinosaur was issued in 1985.

In 1987, in part due to support from fans in Sonic Youth, they signed to SST Records and released what is often considered their best album, You're Living All Over Me. Immediately following that album's release, another band called The Dinosaurs, featuring ex-members of Country Joe and the Fish and Jefferson Airplane, sued them over the use of the name, prompting the addition of "Jr".

Tensions ran high between Mascis and Barlow, and in 1989, after touring in support their third album Bug, Barlow was kicked out of the band. Thereafter, Barlow turned his full attention to his former side-project Sebadoh. "The Freed Pig", the opening track on 1991's Sebadoh III, famously documents Barlow's frustration at Mascis and his treatment within the band.

Murph continued to tour with Dinosaur into the early 1990s, but starting with Green Mind (1991), Mascis (who had started out as a drummer) began to record albums almost entirely on his own. For their later years, Mascis was supported on tour and infrequently on record by George Berz on drums and Mike Johnson on bass.

In 1992 the band was part of the "Rollercoaster" tour, a package tour based on the successful "Lollapolooza" festival, which featured The Jesus & Mary Chain, My Bloody Valentine & Blur. On the 1993 release, Where You Been, the opening track ("Out There") had an accompanying video and was aired on MTV for a short time, as the show 120 Minutes was still popular as a late-night "alternative" video show.

After 1997's Hand It Over, Mascis finally retired the Dinosaur Jr name. In 1999, he released the first of two solo albums under the name J Mascis and the Fog.

In 2004, Mascis regained the master rights to the first three Dinosaur Jr albums from SST, and arranged for their reissue on the Merge label in early 2005. The reissues coincided with the announcement that the original lineup of Mascis, Barlow and Murph was reuniting for a summer tour.

2006 saw the continuation of the Dinosaur Jr reunion tour, as well as the band's first DVD release. A new album is anticipated later in the year. While on tour in New York that year, much of the band's equipment was stolen from outside of their hotel. [1]

Dinosaur Jr's career was chronicled in Our Band Could Be Your Life, a book by Michael Azerrad about several important American underground rock groups during the 1980s, and were one of the curators of 2006's All Tomorrow's Parties festival.

The original line-up of Dinosaur Jr. are to release their first album of new material since 1989. Recorded at guitarist J Mascis' home studio in Amherst, Massachusetts, the currently untitled album is due for a spring 2007 release. Tracks mooted for the new album include 'By The Fire', 'This Is All I Came To Do', 'Back To Your Heart' and 'Stop'.