Section 106 agreements (section 106 of the Town and Country Planning Act 1990 (TCPA 1990)) enable those with an interest in land to ‘by agreement or otherwise’ enter into an obligation to (TCPA 1990, s 106(1)(a) to (d)): • restrict the development or use of the land • require specified operations to be carried out • requiring the land to be used in any specific way, or • require a sum or sums to be paid to the authority As TCPA 1990, s 106 permits the obligation(s) to be given ‘by agreement or otherwise’, the obligation(s) can be made by a unilateral undertaking. Consideration is given in this answer to both. For either an agreement or a unilateral undertaking to be binding on all interests in the land, all those with an interest in the land must be made parties to the agreement, or they must join in the unilateral undertaking.