To determine whether withholding tax is applicable, the Payer has to ascertain that the payment was made to a company or an individual who is Non-Resident in Singapore.

1. Non-Resident Company
   A company is either a tax resident or a non-resident of Singapore. In Singapore, the tax residency of a company is determined by the place in which the business is controlled and managed. “Control and management” is the making of decisions on strategic matters, such as those on company policy and strategy. Where the control and management of a company is exercised is a question of fact. Typically, the location of the company’s Board of Directors meetings, during which strategic decisions are made, is a key factor in determining where the control and management is exercised. Conversely, a company is a non-resident when the control and management of the company is not exercised in Singapore. Do note that the place of incorporation of a company is not necessarily indicative of the tax residence of a company.For more details, you may refer to Tax Residence Status of a Company
2. Non-Resident Individuals and Foreign Professional (Non-Resident Professional)
   Foreign professionals are individuals exercising any profession (i.e. persons other than employees) of an independent nature under a contract for service. For more details, you may refer to Foreign Professionals
3. Non-Resident Public Entertainer A public entertainer performing in Singapore can be exercising a profession, vocation or employment.For more details, you may refer to Non-Resident Public Entertainers
4. Foreign Board Director (Non-Resident Director)For tax purposes, a board director is a member of the board of directors of a company.

For more details, you may refer to Foreign Board Director

The following types of payments attract withholding tax when paid to non-resident companies:

1. Interest, commission, fee in connection with any loan or indebtedness;
2. Royalty or other payments for the use of or the right to use any movable property;
3. Payments for the use of or the right to use scientific, technical, industrial or commercial knowledge or information or for the rendering of assistance or service in connection with the application or use of such knowledge or information;
4. Payments of management fees;
5. Rent or other payments for the use of any movable property;
6. Payments for the purchase of real property from a non-resident property trader;
7. Structured products (other than payments which qualify for tax exemption under section 13(1)(zj) of the Income Tax Act);
8. Distribution of real estate investment trust (REIT). 

Most of these payments are also covered under Sections 12(6) and Section 12(7) of the Income Tax Act.
You may refer to this flowchart on the withholding tax implications for such payments, General Overview of Withholding Tax on Income Deemed to be Sourced in Singapore under Sections 12(6) and 12(7) of the Income Tax Act (PDF, 101KB).