A low-density parity-check (LDPC) decoder architecture that supports variable block sizes and multiple code rates is presented. The proposed architecture is based on the structured quasi-cyclic (QC-LDPC) codes whose performance compares favorably with that of randomly constructed LDPC codes for short to moderate block sizes. The main contribution of this work is to address the variable block-size and multirate decoder hardware complexity that stems from the irregular LDPC codes. The overall decoder, which was synthesized, placed and routed on TSMC 0.13-micron CMOS technology with a core area of 4.5 square millimeters, supports variable code lengths from 360 to 4200 bits and multiple code rates between 1/4 and 9/10. The average throughput can achieve 1 Gbps at 2.2 dB SNR.