Crests (Digimon)

What Are Crests?
After defeating Devimon, the Digidestined were sent to File Island by Gennai to seek the Tags and Crests. The Tags and Crests were scattered throughout DigiWorld by Devimon, after foreseeing his defeat.

The Tags are simply items that the crests are stored in, if the Tag is near its Crest then it reacts by glowing.

Crests are used to let Digimon digivolve past their champion form into ultimate form.

Series One.
To begin with, the Digidestined were seeking Seven crests (one for each Digidestined), however when it was discovered that there was an eighth child, the children discovered that Myotismon already posessed the Eighth Crest.

Each Digidestined has thier own Crest, matching thier personality:

-Crest of Courage - Tai Kamiya and Agumon (First to digivolve into Ultimate Level)

-Crest of Love - Sora Takenouchi and Biyomon (Fourth to digivolve into Ultimate Level)

-Crest of Sincerity - Mimi Tachikawa and Palmon (Fifth to digivolve into Ultimate Level)

-Crest of Hope - T.K. Takaishi and Patamon (Last to digivolve into Ultimate Level)

-Crest of Friendship - Matt Ishida and Gabumon (Second to digivolve into Ultimate Level)

-Crest of Reliability - Joe Kido and Gomamon (Sixth to digivolve into Ultimate Level)

-Crest of Knowledge - Izzy Izumi and Tentomon (Third to digivolve into Ultimate Level)

-Crest of Light - Kari Kamiya and Gatomon (Seventh to Digivolve into Ultimate Level)

Season Two.
In Season Two it is revealed that the Digimon Emperor also had his own crest.

Crest of Kindness - Ken Ichijouji and Wormmon

However, Unlike his predecessors, Ken's crest never re-acted, therefore Stingmon never actually digivolved into his Ultimate form. However, this was probably made up for, by the existence of DNA Digivolution.

Onwards.
Ken is the last digidestined in the anim√© to actually own a crest.

Although Willis's digimon Terriermon digivolves via normal digivolution, there is no evidence to suggest that Willis has a crest.

Although it is revealed Terriermon can digivolve through Golden Digi Eggs. This allows Terriermon to digivolve into a Golden version of Series Three's Rapidmon.