Five years ago we had an idea. What if brands advertised by invitation? Instead of focusing on what happens when people tune out, what if brands focused on what happens when people tune in? We launched an experiment giving users a choice: TrueView. Today, it's our most successful ad format.

The prevailing pessimism when it comes to advertising is that no one wants to watch ads. But what happens if you flip that pessimism to optimism? Will people actually choose to watch ads? Is it possible to create an environment that is better for consumers by eliminating the interruption that characterized video advertising; better for publishers by improving fans' experiences with their content; and better for brands by delivering the ultimate in engaged viewers and only charging for those that choose to watch?

As the handful of brands highlighted here and thousands like them have shown, the answer is a resounding yes. The TrueView ad format on YouTube lets users choose the ads they want to watch, helping to herald a new era of video advertising focused on putting the user first. Today, those choice-based TrueView ads represent 85% of the advertising on YouTube.

Brands on YouTube have answered the challenge of choice with ads worth watching. So worth watching, in fact, that four of the top ten videos on YouTube in 2014 came from brands.

In celebration of TrueView's fifth anniversary, here's a look back at some of the most iconic ads people tuned into over the past five years:

For a timeline of these highlights, check out the infographic below: