In foreign trade business, handling various documents in a standardized and accurate manner is the cornerstone of professional competence. Among them, commercial invoice (CI), proforma invoice (PI), packing list (PL), and purchase order (PO) are core links in the transaction process and are particularly important. This article will clearly explain the definitions and differences of these four for you.

01 CI: Commercial Invoice
It is called "Commercial Invoice" in Chinese. It is a formal document issued by the seller to the buyer (a core document), serving as the basis for both parties' accounting. It details transaction information such as the name of goods, specifications, quantity, unit price, and total price, and also serves as the foundation for calculating customs duties and value-added tax. 
A simple understanding: The "official charge voucher" at the time of shipment, which records the actual goods and amount, is a legally binding "final bill". 

02 PI: Proforma Invoice
It is also known as "Formal Invoice" or "Pre-invoice" in Chinese. It is more like a "draft agreement" and is an informal invoice, usually used in the early stage of a transaction. It mainly provides the importer with transaction information (including description of goods, quantity, unit price, etc.) to facilitate price negotiation and confirmation of transaction conditions between both parties. 
A simple understanding: The "estimated price list + intention confirmation form" before the transaction, listing goods, quantities, estimated amounts, etc., is like a "transaction draft". 

03 PL: Packing List
It is called "packing list" in Chinese. It is a detailed list of goods packaging provided by the seller to the buyer. It is a "physical verification document" used in conjunction with the CI, and has nothing to do with "money", only focusing on "goods". 
For customs clearance verification: The customs needs to confirm through the PL whether the "quantity of goods packaging, gross weight/net weight, volume" are consistent with the CI and the actual goods to avoid "mismatch between goods and documents" (for example, if the CI states 100 pieces and the PL states 90 pieces, the customs will detain the goods for verification). 
For the buyer's receipt verification: After receiving the goods, the buyer can count the quantity and specifications of the products in each package according to the packing list to confirm if there is any shortage or misdelivery. 

04 PO: Purchase Order
This is a "Purchase Order" issued by the buyer to the seller. Once both parties sign it, it becomes legally binding. It locks in key information such as product model, quantity, unit price, delivery date, and payment method, serving as the core basis for the seller's production scheduling, shipping, and account reconciliation. 
A simple understanding: The "purchase order" given by the buyer to the seller is the key document that turns the transaction from "intention" to "substance".

The sequence of these four documents in actual business operations can be regarded as a closely-linked chain: 
1. Transaction Start: Proforma Invoice (PI) The business begins with the buyer's inquiry. After the seller calculates the costs based on the requirements, they issue a proforma invoice (PI) to the buyer. This document is essentially a detailed quotation, specifying product specifications, unit prices, total amount, transaction method (such as FOB), and payment method (such as 30% advance payment). The PI serves as the foundation and basis for all subsequent operations. 
2. Order Confirmation: Purchase Order (PO) If the buyer accepts the terms of the PI, a purchase order (PO) will be issued. The PO is the buyer's formal procurement instruction, and its content is usually consistent with the PI. After the seller signs and confirms the PO, it indicates that both parties have reached a binding contract relationship for this transaction. 
3. Shipping Documents: Packing List (PL) After the seller completes the production and packaging according to the PO, a packing list (PL) will be prepared. The PL serves as the "identity card" of the goods, detailing specific information such as the items, quantity, gross weight, net weight, volume, etc. contained in each packaging box. It does not involve monetary amounts and is mainly used for cargo transportation, counting, and verification. It is usually carried along with the goods or sent to the buyer in advance. 
4. Basis for Collection: Commercial Invoice (CI) After the goods are shipped, the seller will issue a commercial invoice (CI). This is the most crucial document in the entire process, as it lists the final total amount to be collected and serves as the official voucher for the seller to request payment from the buyer. At the same time, the CI is also the core document for the buyer to handle import customs clearance and determine tariffs. 
Process loop: Ultimately, the buyer makes the final payment using the CI, and together with the PL, they declare to the customs and complete the customs clearance and goods pick-up. The entire transaction, from the quotation (PI), contract (PO), physical delivery (PL) to financial settlement (CI), forms a complete loop.