This study presents improved germline Cas9 promoters for homing gene drives in Drosophila. The nanos promoter, while effective in reducing somatic expression, had high embryo resistance due to maternal Cas9 deposition. Eleven other Drosophila germline promoters were tested, with some showing higher drive conversion efficiency and lower embryo resistance. However, none completely avoided somatic expression. Despite this, somatic expression often did not carry significant fitness costs for rescue homing drives targeting haplolethal genes. One promoter led to low drive equilibrium frequency due to fitness costs from somatic expression, while another outperformed nanos, successfully suppressing a cage population. Gene drives are powerful tools for controlling pest insect populations and reducing vector-borne diseases. CRISPR-based homing gene drives convert wild-type alleles into drive alleles in heterozygotes through homology-directed repair. However, resistance alleles can form via end-joining repair, which often mutates DNA sequences and prevents recognition by guide RNAs. Ideal promoters should minimize resistance allele formation and somatic expression. In Drosophila, the nanos promoter avoids somatic expression but causes high embryo resistance. Other promoters, such as zpg and nanos, showed similar performance with much lower embryo resistance and somatic expression. A homing suppression drive with the zpg promoter successfully eliminated an Anopheles cage population. The study tested various Cas9 promoters in Drosophila, finding that some, like zpg and nanos, had lower embryo resistance and somatic expression compared to nanos. These promoters showed better performance in suppression drives. The study also found that the CG4415 promoter with the nanos 3' UTR had the highest drive inheritance rate and lowest embryo resistance. The study highlights the importance of selecting Cas9 promoters that minimize resistance allele formation and somatic expression for effective gene drives. The results suggest that these promoters could be valuable for homing drives in Drosophila and potentially in other organisms.This study presents improved germline Cas9 promoters for homing gene drives in Drosophila. The nanos promoter, while effective in reducing somatic expression, had high embryo resistance due to maternal Cas9 deposition. Eleven other Drosophila germline promoters were tested, with some showing higher drive conversion efficiency and lower embryo resistance. However, none completely avoided somatic expression. Despite this, somatic expression often did not carry significant fitness costs for rescue homing drives targeting haplolethal genes. One promoter led to low drive equilibrium frequency due to fitness costs from somatic expression, while another outperformed nanos, successfully suppressing a cage population. Gene drives are powerful tools for controlling pest insect populations and reducing vector-borne diseases. CRISPR-based homing gene drives convert wild-type alleles into drive alleles in heterozygotes through homology-directed repair. However, resistance alleles can form via end-joining repair, which often mutates DNA sequences and prevents recognition by guide RNAs. Ideal promoters should minimize resistance allele formation and somatic expression. In Drosophila, the nanos promoter avoids somatic expression but causes high embryo resistance. Other promoters, such as zpg and nanos, showed similar performance with much lower embryo resistance and somatic expression. A homing suppression drive with the zpg promoter successfully eliminated an Anopheles cage population. The study tested various Cas9 promoters in Drosophila, finding that some, like zpg and nanos, had lower embryo resistance and somatic expression compared to nanos. These promoters showed better performance in suppression drives. The study also found that the CG4415 promoter with the nanos 3' UTR had the highest drive inheritance rate and lowest embryo resistance. The study highlights the importance of selecting Cas9 promoters that minimize resistance allele formation and somatic expression for effective gene drives. The results suggest that these promoters could be valuable for homing drives in Drosophila and potentially in other organisms.