All the modern giants of advertising still swear by this book. Ogilvy even claimed it changed his life (in advertising anyway, but who knows, advertising is Ogilvy's life). The book is amazing in both its simple and direct approach. It's relatively short, yet packed with information of use to anyone interested in advertising.
Hopkins essentially invented many of the concepts that so many advertisers take for granted today, chief among them what seems like a simple idea: the coupon. And even today, many advertisers fail to get results when they stray from his teachings.
One of the most famous examples of failing to follow his teachings: the "Got Milk" campaign. Sure, it seems clever and it's definitely high profile, but from a marketing standpoint, it's a flop. Milk sales have not moved upward at all despite the fact that milk producers are now several years into the campaign. Want to know why it failed? Read Hopkins's book.
Whether you are an individual considering a career in advertising or an businessperson trying to figure out how best to market your business, start with Hopkins and then move onto the rest.
All advertising before "Scientific Advertising" flows into it; and all advertising after "Scientific Advertising" flows out of it.