As a product of nature diamonds may bear traces of the pressure and processes involved in their formation. These traces may appear on the diamond either externally, or internally and are referred to as "inclusions".

Where appearing internally on the diamond these inclusions may include air bubbles, cracks and non-diamond mineral deposits. Inclusions appearing externally may include scratches, pits and chips.

Not all diamonds have inclusions, and those without, are rare and often the most expensive. Diamonds with inclusions are graded according to the amount of inclusions detected.

Diamonds are graded for clarity under 10x magnification. Grading is allocated to a range of diamonds from "Flawless" to "Included-3" according to the following the following grades:

• FL (Flawless):
  No internal or external flaws;
• IF (Internally Flawless) or LC (Loupe Clean):
  No internal flaws but some surface flaws;
• VVS1-VVS2 (Very Very Slightly Included):
  Tiny inclusions which are very difficult to detect under 10x magnification;
• VS1-VS2 (Very Slightly Included):
  Tiny inclusions which are difficult to detect under 10x magnification;
• SI1-SI2 (Slightly Included):
  Tiny inclusions which are detectable under 10x magnification;
• I1-I3 (Included):
  These inclusions are detectable under 10x magnification, and are also visible to the human eye.

Each diamond's inclusions are unique to that diamond, with no two diamonds displaying the exact same inclusions. The Gemological Institute of America (GIA) diamond grading reports include graphic illustrations of inclusions found in diamonds. These graphic illustrations match the inclusions actually found in the diamonds, providing each diamond with its own "diamond fingerprint".