Yell is reached by the inter-island ferry run by Shetland Islands Council, crossing from Toft on Mainland Shetland to Ulsta on the south end of Yell. The crossing takes around twenty minutes and operates very frequently throughout the day — you rarely wait long. If you're continuing north to Unst, a second ferry runs from Gutcher at Yell's north end to Belmont on Unst, another short hop of similar length. Both services are efficient and reliable even in mixed weather.
There is no direct ferry from Lerwick to Yell. The standard approach is to drive or take a bus north from Lerwick up the Mainland to Toft, then join the ferry queue. The full journey from Lerwick to Burravoe in the south of Yell takes around an hour including the crossing. Driving the length of Yell between the two ferry terminals — south at Ulsta, north at Gutcher — takes roughly thirty minutes on the single main road, and the drive itself is worth doing.