The MX-5 is currently in it's 4th generation of production. The NA, (First gen) NB, (Second Gen) the NC (Third gen) and the ND. (Fourth Gen) These names are derived off of the first two letters of the cars' VIN numbers.
First gen (NA)
The NA was produced from 1989 (As a '90 model) until 1997. It's known for it's pop-up headlights and classic '70's styling.
Second gen (NB)
The NB was produced from 1999 until 2005. The NB is known for it's fixed headlights and more modern styling.
Third gen (NC)
The NC was produced from 2005 (As a '06 model) until 2015. It's known for it's round styling and flared fenders. The NC was the first generation to have an optional power retractable hard top.
Fourth gen (ND)
The ND was introduced in 2015 (As a '16 model) and is still in production today. It has a more aggressive body style and it is smaller and lighter than the NC.
North American MAZDASPEED
The MAZDASPEED MX-5 was produced for only 2 years. ('04 and '05) It had a turbocharged engine that produced 178 HP. While that only beats the NC MX-5's power by around 10 HP, it has 20 more LB-FT of torque. The MAZDASPEED also received a more aggressive suspension, 17 inch Racing Hart wheels and more aggressive body styling via an aero package and black headlight bezels.