First, we should mention that Isaan has a number of spellings and you will run into all them. Some variations are: Issan, Isarn, Isan, Esarn and others. It is pronounced E-Sahn.
Isaan is primarily rural farmland - mostly rice, but it has other crops
such as sugar cane as well. It is the poorest part of the country and
the least visited. The lack of tourists makes it appealing to those
who want an "authentic" Thai experience.
Issan offers a lot of authenticity but does not have the well-known tourist attractions found in the more popular Central, Northern and Southern regions. That
does not mean, however, that there aren't interesting and worthwhile things to see
and experience.
Isaan shares a border with Laos on the North and Northeast and Cambodia on the Southeast. Laotian Culture has had a strong influence in the area for many years and, to a lesser extent, so has Cambodian Culture. Everyone in Isaan speaks Thai, of course, but the majority of people also speak Laotian. There are some significant pockets where Khmer - the language of Cambodia - is spoken.
Other cultural influences,
from both countries, include architecture (especially temples) food, music,
dance and local festivals.
The provinces of Isaan include: Buriram, Chaiyaphum, Kalasin, Khon Kaen, Loei, Mukdahan, Nakhon Phanom, Nakhon Ratchasima (usually called Khorat), Nong Khai, Roi Et, Sakon Nakhon, Si Saket, Surin, Ubon Ratchathani, Udon Thani and Yasothon.
Big cities that have most of the amenities of Bangkok are Khon Kaen, Khorat, Ubon Ratchathani and Udon Thani.
Smaller cities that are more "authentic" but have fewer amenities
are Loei, Roi Et, Si Saket and Surin. Nong Khai, across the Mekong
River from Laos is a bit touristed but a
worthwhile stopover anyway.