What forms is an LLC requiired to file?

It depends on HOW the LLC is registered, because an LLC is a legal entity, NOT a tax entity.

It depends on the situation; Various tax classification options exist for LLCs. "SMLLCs can file as a sole proprietorship, which means the owner can benefit from pass-through taxation. Pass through taxation allows sole proprietors to claim the losses and profits of the business on their tax returns. LLCs filing as sole proprietors must file a Sch C/ Sch SE of 1040; MMLLCs filing as general partnerships should file a Form 1065;. Form 1065, or Sch K-1, shows the partner's share of income, deductions and credits from the business. LLCs, either MMLLC/SMLL, that elect to file as either an S corp or reg C corp file IRS Form 1120S.1120. If the LLC chooses to file as an S corporation, Form 1120S must be filed instead. "The 1120 is the corporate income tax return, and there are no flow-through items to a 1040 from a corporate return," states the IRS. Without the advantage of pass-through taxation, LLC owners are not able to use the expenses of the business to offset personal tax liabilities.