The techniques used in Material Requirements Planning (MRP) include the following:

1. Bill of Materials (BOM): A bill of materials is a list of all the raw materials, components, and sub-assemblies needed to manufacture a finished product. The BOM is used to calculate the material requirements for each product, based on the production plan and the inventory schedule.
2. Master Production Schedule (MPS): A master production schedule is a detailed plan that specifies the quantity of each product that needs to be produced during a specified time period. The MPS is used to calculate the materials requirements for each product, based on the production schedule and the inventory levels.
3. Inventory Status File: The inventory status file contains information about the current inventory levels of raw materials, components, and finished products. It is used to calculate the materials requirements for each product, based on the production plan and the inventory levels.
4. Materials Requirements Planning (MRP) Software: MRP software is a computerized tool that is used to automate the materials planning process. It takes into account the BOM, the MPS, and the inventory status file, and calculates the materials requirements for each product, based on the production plan and the inventory levels. It generates purchase orders or manufacturing orders for the required materials, based on lead times and other constraints.

Overall, the key technique in MRP is the use of computerized software to automate the materials planning process. This helps businesses to plan and manage their materials more efficiently, and to optimize their production processes.