Norwegian Forest Cats are fortunate that the breed standard (the conformance to which defines a Norwegian Forest Cat) is relatively similar throughout the world. Lets start with the similarities to define our basic cat and save the minor details between Cat Clubs for later.
All organizations specify that this is a very slow maturing breed (with FIFe going to so far as to say it should be taken into account). In the case of the Norwegian Forest Cat slow maturing means up to 5 years to reach peak adult size. It also means that kittens do not develop all features, such as guard hairs, until they are nearly competing with adult cats.
I look at FIFe as the base standard for the Norwegian Forest Cat for the sole reason that it was a FIFe Cat Club member which re-introduced the NFO to the world. As such, it has the longest history of showing the NFO.
The FIFe NFO standard tends to be well laid out with minimal but exacting words. Some items like Chin type can be limiting in scope for defining a shape. In the FIFe standard it is only listed as "Firm". This is however more than TICA defines; for which there is no specific criteria.
TICA appears to have the shortest breed standard (at two pages) until it is noted that three of the four pages in the CFA standard is relagated definitions of coat color.
One are the TICA standard notes several times is tempermant. The eyes should have an "Alert expresion" and a specific criteria on Temperment which calls for them to be "Inelligent an dindependent."
CFA is succint in their standard with focusing on the miminum requirements. They cover this precisely by including a disqualification section which set's clear boundaries on what should even be considered.
In recent more recent times I have heard certain Norwegians referred to as modern. This harkens back to the revival of the breed in the 1970's. Traditionally Norwegians were Tabby or Solid colored, with common colors of Black, Orange, and Tortoishell. These we will call the classic. While modern Norwegians maintain that same base coloring; but may also include, dilution (black -> blue, orange -> creme, etc), coat effects (smoke & silver), and coverings (such as white).
There is also a unique genetic extension which causes a special color, Amber, in Norwegian Forest Cats. Amber cats start out black, or regularly colored, and as they grow the black turns to an amber color. Due to the time delay in identification it is important to know if any cats in a breeding program contain the Amber gene. At RebelSkog we do not have amber cats.