In India, GST (Goods and Services Tax) registration is mandatory for certain persons and optional/voluntary for others, depending on the nature of business, turnover, and type of supply. Here's a clear explanation in text format (no tables): Who Has to Register for GST (Mandatory Registration)? GST registration is compulsory for the following categories: 1. Businesses whose aggregate turnover exceeds the threshold limit: For businesses within the same state (intra-state supply): If you sell goods: Registration is required if turnover exceeds ₹40 lakhs (₹20 lakhs for special category states like the Northeast). If you provide services: Registration is required if turnover exceeds ₹20 lakhs (₹10 lakhs for special category states). 2. Inter-State Supply: If you supply goods or services to another state, you must register for GST regardless of turnover. 3. E-commerce Sellers and Aggregators: If you sell through platforms like Amazon, Flipkart, etc., you must register, even if turnover is below the threshold. 4. Casual Taxable Persons: Someone who occasionally supplies goods/services in a taxable territory where they have no fixed place of business (e.g., exhibition stalls, temporary shops) must register regardless of turnover. 5. Non-Resident Taxable Persons: Foreigners or non-residents supplying goods/services in India must obtain GST registration before starting operations. 6. Persons liable to pay tax under reverse charge mechanism (RCM): If you're required to pay GST on behalf of the supplier, you must register. 7. Input Service Distributors (ISD): Entities distributing input tax credit among branches must register. 8. Agents supplying on behalf of other taxable persons: Commission agents, brokers, or intermediaries also require registration. 9. Persons required to deduct TDS or collect TCS under GST: Government departments and e-commerce platforms that deduct tax must register. 10. Others notified by the government: The government may notify specific businesses or categories that must register. Who Can Register Voluntarily? Even if not required by law, you can opt for voluntary GST registration to: Claim input tax credit (ITC) Operate with larger businesses Improve business credibility Once registered voluntarily, you are treated as a regular taxpayer and must follow all GST compliance rules (like filing returns, paying tax, etc.). Penalties for Not Registering (When Required) If you are liable but fail to register, the tax authorities can impose a penalty of 100% of the tax due or ₹10,000, whichever is higher. You may also be liable to pay GST from the date you were supposed to be registered, along with interest. Conclusion You must register for GST in India if: Your turnover exceeds the threshold based on your business type and location You do inter-state supply, sell online, or are covered under special categories (like agents, non-residents, RCM, etc.) If you're unsure, it's safer to consult a GST practitioner or chartered accountant to avoid non-compliance.