No musical genre exists in a vacuum. Not all of the bands that have been a part of the history and development of progressive rock are necessarily progressive rock bands themselves. This is why progarchives has included a genre called prog-related, so we could include all the bands that complete the history of progressive rock, whether or not they were considered full-fledged progressive rock bands themselves. 

There are many criteria that the prog-related evaluation team considers when deciding which bands are considered prog-related. Very few bands will meet all of this criteria, but this list will give an idea as to some of the things that help evaluate whether an artists is prog-related or not. 

1) Influence on progressive rock - The groundbreaking work of artists like Led Zepplin and David Bowie affected many genres of rock, including at times progressive rock. Although both of these artists created rock music in a dizzying array of genres, both contributed to the ongoing history of progressive rock several times within the span of their careers. 

2) Location - Progressive rock did not develop at the same time all over the world. It may surprise some people that as late as the mid-70s the US had very few original progressive rock bands that did not sound like exact copies of British bands. Journey was one of the first US bands to present a uniquely American brand of prog-rock before they eventually became a mainstream rock band. We have collaborators from all over the world who tell us which bands helped the progressive rock scene develop in their corner of the globe, even if those bands were like Journey and were known more for being mainstream rock bands. 

3) Members of important progressive rock bands - Although most of the recorded solo output of artists like Greg Lake and David Gilmour falls more in a mainstream rock style, their contributions to progressive rock in their respective bands insures them a place in our prog-related genre. 

4) Timeliness - Like many genres, prog-rock has had its ups and downs. In the late 70s and early 80s prog-rock was barely a blip on the radar. During this time artists such as David Bowie and Metallica released albums that captured key elements of the spirit of prog rock and did so while contributing their own original modern elements to the mix. 

5) Integral part of the prog-rock scene - Sometimes you just had to be a part of the scene during a certain time period to understand how some bands fit with the prog rock scene of their time. Although Led Zeppelin, Black Sabbath and Wishbone Ash may seem like mere hard rock bands, in their time they stood apart from other hard rockers with their more serious lyrical content and more developed compositions. Put simply, in the early 70s every prog-rock record collector usually had full collections of all three of these artists. These three bands were very much part of the prog-rock scene without being total prog-rock bands them selves. 

6) Influenced by progressive rock - From the late 60s till about 1976 the progressive tendency was in full effect in almost all genres of music. Once again, as we enter the second decade of the 21st century a melting pot of prog-metal, math-rock, progressive electronics and post-rock influences have once again made a progressive tendency in rock music almost more a norm than a difference. Yet in other periods of musical history receiving influence from progressive rock could really set a band apart and make them worthy of our prog-related category. 

Being influenced by progressive rock is hardly the only factor we look at, and in some periods of musical history it is almost meaningless, but still, it is almost a given that most of the artists listed in prog-related were influenced by the development of progressive rock. 

7) Common sense - Nitpicking over the above listed criteria is not necessarily the correct way to evaluate a band for prog-related. Sometimes you just have to use some common sense and look at the big picture. 

A very good way to describe prog-related would be to imagine an exhaustive book that covered the history of progressive rock. Would such a book include references to led Zeppelin's 'Stairway to Heaven', David Bowie's 'The Man Who Sold the World' or Queen's 'Bohemian Rhapsody'? Probably so. 

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