Cyclo-cross has been around since the 1940's or so, and was originally a way for road racers to maintain their fitness level through late fall and early winter. It was started in Europe where it has remained consistently popular. If you look at world class mountain bike races from the early-mid '90s onwards, the Americans (who invented mountain bike racing) are no longer dominant. Europeans win almost all the races. It's not because they picked up on mountain bike racing quickly, it is because of their background in Cyclo-cross. Several mountain bike world champions in recent years have been past Cyclo-cross champions.

The race course is usually a mix of grass fields, dirt roads, relatively short asphalt sections (if any), some sand, some mud or stream crossings and several forced dismounts and running sections. The natural obstacles in 'cross courses are often less severe than in mountain bike courses, but many mountain bike racers will say that Cyclo-cross is physically harder and more painful than mountain bike racing, and of course it's very different from riding on the tarmac.

Forced dismounts and running sections are the thing that really sets 'cross apart from other types of racing. Barricades 10-18in high are erected in the course in sets of between two and six, and they are spaced closely enough together to prevent bunny hopping.

There's a certain grace in the way an accomplished 'cross racer can approach a set of barricades at full speed, dismount and begin running while shouldering his or her bike, then jump the barricades, then setting down the bike, remount and pedal off. Remember that this all happens in continuous, fluid motion and there is very little reduction in speed. Other popular forced dismounts are short, very steep climbs that can't be ridden, or, sometimes, stair climbs.

A classical Cyclo-cross bike looks very much like a road bike, but there are significant differences between the two. The rear triangle and fork have more clearance to allow for wider tires, and to help reduce mud buildup. 'Cross tires are wider than road tires, though the tyres a rider chooses will depend on the course and how wet, muddy or sandy it is.

'Cross bikes have cantilever brakes for mud clearance and control in messy conditions. The handlebars are road-style drops ­ it's arguable whether these affect control one way or another, but they reflect the sport's origins as off-season training for road racers as much as anything else.

Almost all 'cross races allow mountain bikes as long as they don't have forward facing bar-ends, which are banned because of safety concerns during a crash. Most beginners will first try 'cross on a mountain bike due to cost, availability and improved stability. However, many accomplished "A" category 'cross racers will always ride a mountain bike, while others sometimes ride a mountain bike depending on the course and conditions.

The best way to understand Cyclo-cross is to go and watch a race. Make sure to bring your bike (a mountain bike is fine) so you can ride the course before the first race. Looking at a 'cross course is always confusing at first because they are typically set up with ribbons and flags marking the course, which serpentines over a relatively small area. Of course, creating a  course in a relatively small area makes securing a venue and setting up/tearing down a course a little easier AND the smaller courses makes it great for spectators!

C'mon!  Try it!