(15)It should be clarified that groups of economic operators, including where they have come together in the form of a temporary association, may participate in award procedures without it being necessary for them to take on a specific legal form. To the extent this is necessary, for instance where joint and several liability is required, a specific form may be required when such groups are awarded the contract. It should also be clarified that contracting authorities should be able to set out explicitly how groups of economic operators are to meet the requirements concerning economic and financial standing as set out in this Directive, or the criteria relating to technical and professional ability, which are required of economic operators participating on their own. The performance of contracts by groups of economic operators may necessitate setting conditions which are not imposed on individual participants. Such conditions, which should be justified by objective reasons and be proportionate, could for instance include requiring the appointment of a joint representation or a lead partner for the purposes of the procurement procedure or requiring information on their constitution.