The Income Tax Act, 1961 contains special provisions relating to the assessment of companies. These provisions specifically deal with the taxation of income earned by companies, including their computation, assessment, and related matters. Some key aspects of these special provisions include:

1. Assessment of Total Income: The Act lays down the rules for computing the total income of a company, which includes income from various sources such as business or profession, capital gains, interest, dividends, royalties, and other income.
2. Rates of Tax: The Act specifies the applicable rates of tax for different categories of companies. For example, domestic companies and foreign companies are subject to different rates of tax on their taxable income.
3. Presumptive Taxation: In certain cases, the Act provides for presumptive taxation for companies engaged in specific types of businesses. This means that the income of such companies is deemed to be a certain percentage of their turnover or gross receipts, and they are taxed accordingly.
4. Minimum Alternate Tax (MAT): The Act contains provisions for the imposition of Minimum Alternate Tax (MAT) on companies. MAT ensures that companies, especially those claiming various deductions and exemptions, pay a minimum amount of tax, thereby preventing the erosion of the tax base.
5. Tax Incentives and Exemptions: The Act provides for various tax incentives, deductions, and exemptions available to companies. These may include deductions for research and development expenses, investment in certain sectors or activities, incentives for startups, and exemptions for income earned from specified sources.
6. Advance Tax and TDS: The Act mandates companies to pay advance tax on their estimated income during the financial year. It also requires companies to deduct tax at source (TDS) from certain payments such as salaries, interest, dividends, and payments to contractors and professionals.
7. Assessment Procedures: The Act lays down the procedures for the assessment of companies by the tax authorities. This includes filing of returns, scrutiny assessments, reassessments, and appeals.
8. Transfer Pricing Regulations: For multinational companies, the Act contains provisions related to transfer pricing regulations to prevent tax avoidance through manipulation of prices in transactions between related parties.

These are some of the key provisions relating to the assessment of companies under the Income Tax Act, 1961. The Act is regularly amended to reflect changes in tax policies and to address emerging issues in the taxation of companies.