Firstly, you need to decide just what type of 3D you want to shoot. Serious competition, or just to practice and have fun, while at the same time practicing for crossbow hunting. Once that has been decided, one needs to go to the sanctioning body to study the rules, WCSA, NFAA, NAA, ASA, or IBO. They all have different rules regarding crossbow equipment. The two most popular organizations that most will come in contact with is ASA and IBO. The rules differ slightly between these organizations, but enough that serious competitors will want a crossbow for each. I'll not go into the specific rules here, as one can go to the respective web sites and read for themselves. I am aware that there will be a rule change for ASA crossbow class for the upcoming year, so do your homework. IBO rules are nearly anything goes, compared to ASA rules which has speed restrictions. Once you know the rules for the venue you have interest in, study just what is out there that is legal. If you already have a crossbow, give it a try and see how it works for you. If you're just shooting for fun, you probably don't need any other equipment at this time. However, be careful, you just might get bit by the 3D bug, and want a crossbow that is setup specifically for one or more of the ruling bodies. For further details about Crossbow please see http://www.crossbownation.com/.