Trade body Salmon Scotland and local companies, Cooke Aquaculture Scotland, and Scottish Sea Farms, are sponsoring the four-day event as Host Port Associates.
Sailing vessels are already arriving in Lerwick harbour on as part of a route including Aberdeen, Hartlepool, the Dutch city of Den Helder, and Fredrikstad in Norway.
Thousands of people are expected to join in the festivities, as hundreds of young sailors start to arrive on as many as 37 tall ships.
The event will mark the third time the Tall Ships fleet has been hosted in Lerwick after visits in 1999 and 2011.
The tall ships make a return crossing of the North Sea, departing Lerwick on Saturday bound for Arendal in Norway.