Cream Ale is classified by the BJCP as a “Hybrid Beer”: category 6A. It’s classified as a hybrid because it was originally developed as an ale version of the American light lager that was popular in the latter half of the nineteenth century:

An ale version of the American lager style. Produced by ale brewers to compete with lager brewers in the Northeast and Mid-Atlantic States. Originally known as sparkling or present use ales, lager strains were (and sometimes still are) used by some brewers, but were not historically mixed with ale strains. Many examples are kräusened to achieve carbonation. Cold conditioning isn’t traditional, although modern brewers sometimes use it.

There’s a bit of murkiness surrounding the issue; I’ve read that Cream Ales variously were:

• Brewed with ale yeasts but cold-conditioned like lagers;
• Brewed with lager yeast at ale temperatures;
• Brewed with a blend of ale and lager yeasts;
• A blend of ale and lager (finished products).

Randy Mosher in Radical Brewing offers some insight:

As the American brewing industry shifted into the hands of German immigrants familiar with the Altbiers (ales) of Cologne/Köln, brewers cast pale ales in a Continental mold rather than an English one. To my mind, there is little theoretical difference between Kölsch, cream ale, and blonde ale. (p. 80)

And:

The cream ale style is a kind of amalgam of the English-derived American ale style, as brewed by German brewmasters in American lager breweries. It’s my view that many of them simply applied their experience with German ales such as Kölschbier, and voilà, Cream Ale. (pp. 90-91)

From a style and recipe formulation perspective, we’re looking at a very light ale, yellow to gold in color, and generally of “session beer” alcohol levels—anywhere from 4% to 6% and possibly higher. It’s mild on the tongue, crisp and refreshing (often from cold-conditioning), a good lawnmower or summertime beer.

Brewing these beers with corn and/or sugar as an adjunct is acceptable, and even common—and keeping with the style’s historical roots. Understandably, it’s this fact that also gives people a bit of a hang-up when confronting the style: corn is considered to be less-than-desirable in beer—it’s the kind of cheap grain the megabreweries will use in their beers, for instance, and we all know what sort of stigma that carries.

Using corn sugar in a (homebrewed) recipe for Cream Ale is acceptable, up to 20% of the fermentables. When I was formulating my own Cream Ale recipe I settled on one pound of corn sugar and four pounds of dried malt extract, and that seems to work out well.

Of course, many brewers are brewing all-malt version of the style and are foregoing the corn altogether.

Finally, for the numbers-and-stats people, here are the BJCP’s guidelines for the style (you know, if you’re planning on brewing for competition or anything. If not, carry on):