A request for offer, commonly abbreviated to RFO, is a structured invitation to suppliers for the supply of products and/or services.

A Registration of Interest. Also known as ROI.

RFD - request for documentation

request for applications RFA

expression of interest  (EOI)

A request for tender is a structured invitation to suppliers for the supply of products and/or services. It's also abbreviated to RFT.

As a consequence of the scale and complexity of the tender process the majority of RFT’s are published by government sector agencies at the local, state and federal levels. Companies in the infrastructure and utilities sectors may also periodically publish RFT’s

A request for information is a standard business process whose purpose is to collect written information about the capabilities of various suppliers. Normally it follows a format that can be used for comparative purposes. Also known as RFI.

A Request for Quotation is a document issued when an organization wants to buy something and chooses to make the specifications available to many other companies so they can submit competitive bids. A request for quotation is a standard business process whose purpose is to invite suppliers into a bidding process to bid on specific products or services. It's Also known as: RFQ, RFP, Request for Proposal.

A request for proposal is an invitation for suppliers, often through a bidding process, to submit a proposal on a specific commodity or service. A bidding process is one of the best methods for leveraging a company's negotiating ability and purchasing power with suppliers. The request for proposal process brings structure to the procurement decision and allows the risks and benefits to be identified clearly upfront. The request for proposal purchase process is lengthier than others, so it is used only where its many advantages outweigh any disadvantages and delays caused.

As a businessperson, you will inevitably have to write many request letters. The need for information or special favors, services, or products arises daily in almost every type of business. The reasons for writing a request letter are diverse: