"There's a lot of good competition this year," said 'Herbal Santa' a longtime marijuana smoker from Orange Country, California, who, when asked for his name only offered 'Jim'.
Organisers said they expected about 3,500 participants.
The week-long Cannabis Cup is spread out at various coffee shops throughout Amsterdam, although the main events are held in a club on the outskirts of the city, tucked behind a McDonald's fast-food restaurant and a do-it-yourself store.
The event coincides with the annual US Thanksgiving holiday, allowing participants from across the Atlantic to spend a week's holiday in Amsterdam.
The event was started in 1987 by Steven Hager, the editor of New York-based magazine High Times that advocates the legalisation of cannabis, and has become a key annual event among cannabis-orientated business and for many pot smokers.
Judges pay a fee of up to $200 to participate in selecting the winners with their task to examine the potency, taste, smell, curing and overall experience of various herbs.
Marijuana is technically illegal but has been decriminalised and is tolerated in the Netherlands, where it is sold in small quantities in "coffee shops."
"People should come to peace together and smoke," said Arjan Roskam, owner of the Green House Seed Co., whose marijuana strains have won 31 Cannabis Cup prizes over the years. His coffee house is a frequent destination for visiting celebrities.
"You see people from 18 to 80 having a good time," said Roskam. "It's a very friendly gathering