The pilot will run for two-and-a-half years
Low-cost ferry fares are being piloted on all routes to and from the Western Isles from Sunday.
The Scottish Government trial of road equivalent tariffs (RET) will run for two-and-a-half years.
RET bases the cost of travelling on the equivalent distance by road. It will see some fares cut by half.
The SNP made lowering the cost of trips to the isles, which have been seen as a barrier to economic growth, a key commitment in its election manifesto.
There have been complaints from other islands groups, such as Orkney and Shetland, that the pilot only covers the Western Isles.
Welcoming the launch of the scheme, Transport Minister Stewart Stevenson said: "For years, our remote and fragile communities have been expressing concerns about the affordability of ferry travel and the impact this has on islanders.
"Expensive ferry fares can be damaging, not only to our local economies, but to our national economy. We want to take action to address this.
"This is the first pilot which has sought to overhaul the way fares are calculated and the aim is to establish a cheaper and fairer system for ferry users right across the country.
"While initially focussing on a pilot on routes to the Western Isles, we want this test case to pave the way for cheaper fares for all our island communities. The final phase of the study will involve a full evaluation of the pilot exercise and offer options for rolling the scheme out to our other islands.
"This pilot could open the door to a fairer, cheaper system for every ferry user in Scotland."