The Longitudinal Database of Quarterly Census of Employment and Wages (QCEW) links quarterly reports of employment and total wages of all nonfarm establishments covered by State Unemployment Insurance. QCEW uses two types of linkage: deterministic and probabilistic. Deterministic linkage is performed by SESA IDs - a combination of state FIPS code, Unemployment Insurance Number, and Reported Unit Number. The remaining establishments, those not linked by SESA IDs, are linked by a probabilistic method (weighted matching), based on the Fellegi and Sunter theory. This paper performs and evaluates both deterministic and weighted linkage. Recommendations for weighted linkage are given.