Blade (Also called a Mill Grinder) - uses a sharp metal blade that spins around at a high rpm to chop coffee bean into grounds. The longer you grind, the smaller the grounds. Size of grounds will vary when using a blade grinder, which will affect the brewing consistency. (Shaking the grinder while it is grinding to get more grounds in contact with the blade may produce more consistent results.) Also, blade grinding produces heat, which can potentially burn the grounds.

Blade grinders produce coffee grinds that are suitable for drip coffee makers, but are generally not recommended for use in espresso machines.

Burr - uses a metal, revolving grinding wheel to crush the coffee beans into grounds. The space between the grinding wheel and either a non-moving surface or another grinding wheel determines the fineness of the grind. Burr grinders produce a more consistent grind, which provides a more even surface area for extraction of flavor during the brewing process, and allows for a more even wetting and packing of the grounds. Because less heat is produced, burr grinding minimally affects the taste of the coffee compared to blade grinding.

There are two types of burr grinders:
Wheel Burr or Flat-Plate - as a general rule, they are less expensive than conical burr grinders. The burrs are plate-shaped and lie atop each other. The grinding burrs spin very fast (10,000 to 20,000 rpm), and create a grind well-suited for use in an espresso machine. Wheel burr grinders are noiser (and sometimes messier) then conical burr grinders, and they can create a bit more warmth in the ground coffee.
Conical Burr - the best grinder for producing small and very consistent grounds. With an intricate design of the steel burrs and high gear ratio, the speed of the burrs can be reduced to below 500 rpm. With the lower speed, more flavor and aroma can be retained in the coffee. The conical burr grinder is the most ideal type of coffee grinder for those that love the flavor in their gourmet coffee. A conical burr grinder is also the best choice for grinding oily or flavoured coffees, as it's not as likely to clog.