Loss carryforward restrictions limit use of historic losses after changes in firm or company ownership unless strict continuity conditions are met. Section 119 bars carry forward and set off of losses where the taxpayer's identity changes: for firms, losses proportionate to a retired or deceased partner's share that exceed that partner's profit share cannot be carried forward; where a business is succeeded otherwise than by inheritance, only the original loss incurring person may carry forward losses. For closely held companies, prior year losses are disallowed after shareholding change unless substantially the same persons beneficially hold controlling voting power at the tax year end, with an exception for eligible startups subject to shareholder continuity and a ten year incorporation limit; specified exceptions and definitions are provided.