In the Philippines, the Bureau of Internal Revenue (BIR) mandates that every person—natural or juridical—intending to engage in business or the practice of a profession must register with the appropriate Revenue District Office (RDO). This process culminates in the issuance of BIR Form 2303, or the Certificate of Registration (COR), which serves as the official permit to operate for tax purposes.

Failure to comply with these requirements before commencement of operations can lead to hefty "compromise penalties" for late registration.

1. Who Must Register?

The requirement applies to two primary categories of individual taxpayers:

Self-Employed Professionals: Licensed professionals (lawyers, doctors, CPAs) and non-licensed professionals (freelancers, consultants, athletes).
Sole Proprietors: Individuals operating businesses under a Department of Trade and Industry (DTI) trade name (e.g., sari-sari stores, online shops, restaurants).

2. Documentary Requirements

The specific documents vary slightly depending on whether you are a professional or a business owner, but the core requirements generally include:

For Professionals (Licensed and Non-Licensed)

BIR Form 1901: The application form for registration.
Government-issued ID: Any valid ID (Passport, Driver’s License, etc.) showing the applicant's name, address, and birthdate.
Professional Tax Receipt (PTR) or Occupational Tax Receipt (OTR): Issued by the local LGU/City Hall where the profession is practiced.
PRC ID: For licensed professionals.
Proof of Address: Such as a lease contract (if renting an office) or a Title/Tax Declaration (if owned).

For Sole Proprietors (Business)

BIR Form 1901: Application form.
DTI Certificate of Registration: The approved trade name.
Mayor’s Business Permit: Or at least the application for the Mayor’s Permit (though many RDOs now allow the BIR process to happen simultaneously or prior to the final Mayor's Permit).
Proof of Address: Lease contract or proof of ownership of the business site.

3. The Registration Process

Submit Documents: File the required forms at the RDO having jurisdiction over the place of business or the taxpayer’s residence.
Pay the Annual Registration Fee (ARF): As of recent tax law updates (specifically the EASE of Paying Taxes Act), the ₱500 Annual Registration Fee has been abolished. Taxpayers no longer need to pay this annual fee.
Attend the Initial Briefing: Many RDOs require new registrants to attend a short seminar regarding their tax obligations and deadlines.
Issuance of the COR (Form 2303): Once processed, the BIR will issue the Certificate of Registration and the "Ask for Receipt" Notice (Notice to the Public).

4. Post-Registration Requirements

Securing the COR is only the first step. To fully "engage in business," a taxpayer must also complete the following:

Authority to Print (ATP) Invoices: Taxpayers must apply for BIR Form 1906 to print official invoices or receipts. Under the EOPTA, the term "Sales Invoice" is now the primary document for both goods and services.
Registration of Books of Accounts: Taxpayers must have their accounting books (Journal, Ledger, etc.) stamped by the BIR. These can be manual books, loose-leaf, or computerized accounting systems (CAS).
Display Requirements: The COR and the "Ask for Receipt" notice must be conspicuously displayed at the place of business.

5. Tax Obligations of Registrants

Once registered, the taxpayer is subject to specific compliance requirements depending on their chosen tax regime:

Graduated Income Tax: Taxed based on the progressive tax table (0% to 35%), with the option for Itemized Deductions or a 40% Optional Standard Deduction (OSD).
8% Flat Tax Rate: Available to individuals whose gross sales/receipts do not exceed the VAT threshold (₱3,000,000). This is in lieu of both Income Tax and Percentage Tax.
Value Added Tax (VAT) or Percentage Tax: Depending on the annual gross sales.

Summary Table

Requirement	Description
Primary Form	BIR Form 1901
Primary Output	Certificate of Registration (Form 2303)
Books of Accounts	Must be registered and maintained
Invoices	Must be issued for every sale of service or goods
Compliance	Monthly/Quarterly/Annual filing regardless of income