The easiest way to recognise the importance of Drawn & Quarterly is to imagine it had never existed.

Imagine that 25 years ago Montreal's Chris Oliveros decided not to set up a comic company. What might that have meant? That we might never have seen Julie Doucet's Dirty Plotte, Joe Matt's Peepshow, Seth's Palookaville or Chester Brown's The Playboy for a start. Just think how impoverished the autobiographical comic genre would be as a result.

Without D&Q would we know about cartoonists such as Japan's Yoshihiro Tatsumi, the master of gekiga, who sadly died earlier this year, or Israel's Rutu Modan? Would we have even heard of Guy Delisle, Michael DeForge or Kate Beaton? Would Lynda Barry still be in print? (And if not, how much of an artistic act of vandalism would that be?) What would the New Yorker do without the cover talents of Adrian Tomine whose comic Optic Nerve is surely now recognised as one of the key Generation X texts.

And maybe you can go further. Would Jonathan Cape in both the US and the UK have pursued an interest in the graphic novel medium without the D&Q example? (And in the UK some of D&Q's titles)? Would we now have a busy, exciting cadre of British alternative comic publishers such as Blank Slate, Nobrow and Self Made Hero if D&Q hadn't proved it was possible in the first place?

And would the wider world, which, over the last 10 years, has finally started to take the graphic novel form seriously, be talking about it in the media and stocking it in book shops without D&Q championing innovative cartoonists and presenting them in such an elegant and thoughtful manner?

Leafing through the mammoth bulk of Drawn & Quarterly: Twenty-Five Years of Contemporary Cartooning, Comics, and Graphic Novels - a monstrous 776 pages of cartoons, essays, photographs and illustrations - is to be reminded how essential the publisher has been over the last quarter century. And how fortunate we are still to have it. As Sean Rogers' opening essay, A History of Drawn & Quarterly, makes clear, in the early years there were times when it was touch and go. Rival Montreal publisher Black Eye, Michel Vrana's much-lamented comic imprint which did so much to push Drawn & Quarterly's design ambition with its own presentational skills, went out of business in 1998. Drawn & Quarterly at times survived by the skin of its teeth.

Times change. It's now in a position to publish this huge celebration of its own story. And, yes, the result is ever so slightly boosterish, but if anyone has earned the right to pat themselves on the back then it is Oliveros, his colleagues and the cartoonists.

The book is a giant pick-and-mix of comic strips (some old, some new), running alongside appreciations of various D&Q cartoonists from such literary types as Jonathan Lethem, Margaret Atwood and Lemony Snicket. And it's all, as you would expect, impeccably presented.

What will you learn? That Margaret Atwood reads Kate Beaton's cartoons in the bathroom. That Lethem has never paid for sex and that if the cartoonist Doug Wright wasn't Canadian he would probably be as famous as Charles Schulz (man, could Doug draw).

But set aside the appreciations of Wright, Tove Jansson and Denys Wortman (man, could Denys draw too; why have I never heard of him?), and this is a book about where we are now.

If you were looking for a primer for contemporary comic strips this is the perfect place to start, branching out from the autobiographical strips of Seth and Chester Brown to Marc Bell's queasy E-numbered surrealism and Genevieve Castree's gorgeous, intricate Blankets Are Always Sleeping, a strip that riffs on a repeated single-panel design full of duvets and anxiety, to the primary coloured simplicity of Anouk Ricard's comic - in both senses - strip, The Experts. There is so much out there and so much of it is good. This is what we would have lost if D&Q never existed.

Oh yes and this book will make you laugh. On page 626 cover artist Tom Gauld (he's Scottish, you know) tells a story about attending Comic-Con in 2013, where he ended up in a bar with a couple of D&Q staffers and cartoonist Lisa Hanawalt. He was interrupted by a couple of "slightly drunk" young men. "One said to me," he recalls, "'Hey man, we just wanted to know what you've done to get these three chicks to yourself.' I can't exactly remember what I replied but in a perfect world it would have been, 'All you need to know sir, is that I am a Cartoonist.'"

Drawn & Quarterly, 25 Years of Contemporary Cartooning, Comics and Graphic Novels is priced £30.