A Single Member LLC is a business structure that emerged in the 1990s. Over time, it has become recognized in all States. As the name implies, an Single Member LLC has a single owner. Because income from an Single Member LLC isn't divided (as it would be for a partnership or a multiple member LLC) there are no separate taxes to file with the IRS. The IRS treats an Single Member LLC just like a sole proprietorship. (This isn't necessarily true for State level taxation.)
This brings up one disadvantage of a Single Member LLC – the possibility that the company's assets will be taken when a suit arises from the personal – non-business – actions of the single owner. Case law for multiple member LLCs is clear, but because Single Member LLCs are newer, the law in some States is less so. For instance, what happens when the owner of a Single Member LLC dies or goes personally bankrupt? Can the company assets be transferred in the same manner as a simple asset? The arguments revolve around how legally different a Single Member LLC is from a sole proprietorship. This also highlights the importance of keeping Single Member LLC assets and liabilities separate from personal – excellent record keeping and attention to formal rules is key.