The difference is sizeable to say the least. Price, build quality, capabilities, resolution, the list of differences goes on. Let's start with the D70 which has long been discontinued and replaced by the D70s, D80 and now the D90 which itself is facing replacement in the not too distant future.The D70 was Nikon's first sub-$1000(US Dollars) DSLR and was introduced in 2004. It was a 6mp camera and image quality is good even by today's standards as long as you stay below ISO 800. Compared to the current D90, the D70 is also a little slow, doesn't offer Live View or video and has a rather small rear LCD. No DSLR on the market today offers less than 10mp resoluton where as this camera is "only" 6mp but, the reality is, 6mp is plenty so I wouldn't hold that against this camera unless you need more latitude for cropping or make unusually large prints. If you are looking to buy your first DSLR and you have a tight budget, this might be the right camera for you.The D700 is a different beast entirely. It was Nikon's second full-frame DSLR. This means that unlike the D70 and every Nikon DSLR prior to the D3 (Nikon's first full-frame DSLR), the imaging sensor in this camera matches the dimensions of a frame of 35mm film. Nikon calls this their "FX" format where as the other DSLRs are "DX" format and have sensors that are roughly half-sized by comparison. The D700 is really a professional's camera. The D700 doesn't have easy scene modes like the D70 and the current consumer models (Nikon D3000, D5000 and D90). It also has an advanced 51-point autofocus system that is considered the best in the business at the moment. Despite being a 12mp, full-frame DSLR, the D700 is also a very fast camera compared to the D70. It is capable of shooting up to 5 frames per second or 8 frames per second with an optional battery grip attached. Among the current crop of full-frame DSLRS (there are only seven on the market at this time and three of them belong to Nikon), the D700 easily represents the best value for those shooting in low-light or shooting sports.