The increased penetration of variable energy resources in electric power markets has increased the volatility of net load (i.e., load minus non-dispatchable generation) as well as the frequency of strong ramp events. This, in turn, has led system operators to explore potential new products and market design features encouraging flexible service provision to enhance net load following capability. This talk will report on a new form of swing (flexible) contracting that permits greater flexibility in service provision. Roughly, a swing contract for the co-provision of energy and reserve services is a contract whose contractual terms permit a diverse spectrum of services to be offered as ranges of values rather than as point values, thus permitting greater flexibility in their real-time implementation. These offered services might include, for example, ranges for possible start-up times, durations, power dispatch levels, and ramp rates. Another important attribute of swing contracting is that it permits separate market-based compensations for service availability and service performance. The offer price of a cleared swing contract can compensate a contract issuer for service availability costs (e.g., start-up, no-load), while the service performance payment method included among the terms of the contract can ensure that the contract issuer is fully compensated ex post for the costs of any actual services rendered in real-time operations (e.g., energy delivery, power mileage). This talk will also report on the development of a new optimization formulation permitting the market clearing of swing contracts. This new optimization formulation is a mixed integer linear programming (MILP) formulation expressible in analytic terms. It can be solved using the same MILP solution software currently in use for standard Security-Constrained Unit Commitment (SCUC) optimization formulations. A numerical example will be used to illustrate the implementation of this new optimization formulation for the day-ahead market clearing of swing contracts.