SHELXT is a new computer program for solving the phase problem in single-crystal reflection data expanded to the space group P1. It uses a dual-space algorithm to account for missing data and extend resolution. All space groups in the specified Laue group are tested to find the one consistent with the P1 phases. After applying origin shifts and space-group symmetry, the solutions are further refined, peak searches are performed, and elements are assigned to best fit the integrated peak densities. For non-centrosymmetric space groups, a Flack parameter is calculated, and the structure is inverted if necessary. The structure is then assembled to maximize connectivity and centered optimally in the unit cell. SHELXT has successfully solved many thousands of structures and is optimized for multi-processor computers. It is not suitable for severely disordered or twinned structures because it assumes the structure consists of atoms. The phase problem is solved using dual-space methods, starting with a Patterson superposition. The data are merged according to the Laue group and expanded to P1. The dual-space recycling begins with a Patterson superposition minimum function, and the modified structure factors are used for further refinement. The random omit procedure is used to reduce model bias by deleting a small part of the structure and refining the rest. This is implemented differently in SHELXT due to the lack of a model at the P1 stage. The program determines the space group and origin shift by testing all possible space groups in the specified Laue group. The figure of merit α is used to evaluate the best solution. The chemical figure of merit CHEM is calculated by searching for bond angles and assigning elements based on integrated densities. The combined figure of merit CFOM is used to select the best solution. After assigning elements, an isotropic refinement is performed, followed by the determination of the Flack parameter and inversion of the structure if necessary. The structure is then built by clustering atoms and optimizing the position in the unit cell. Examples show SHELXT's effectiveness in solving various structures, including organoselenium compounds and pseudo-centrosymmetric structures. The program is available for free to academics and is suitable for multi-CPU computers. It has been tested on a large number of structures, with a high success rate in identifying the correct space group and element assignments. The program is recommended for use with caution, as incorrect element assignments can occur, especially in cases with disordered solvent molecules.SHELXT is a new computer program for solving the phase problem in single-crystal reflection data expanded to the space group P1. It uses a dual-space algorithm to account for missing data and extend resolution. All space groups in the specified Laue group are tested to find the one consistent with the P1 phases. After applying origin shifts and space-group symmetry, the solutions are further refined, peak searches are performed, and elements are assigned to best fit the integrated peak densities. For non-centrosymmetric space groups, a Flack parameter is calculated, and the structure is inverted if necessary. The structure is then assembled to maximize connectivity and centered optimally in the unit cell. SHELXT has successfully solved many thousands of structures and is optimized for multi-processor computers. It is not suitable for severely disordered or twinned structures because it assumes the structure consists of atoms. The phase problem is solved using dual-space methods, starting with a Patterson superposition. The data are merged according to the Laue group and expanded to P1. The dual-space recycling begins with a Patterson superposition minimum function, and the modified structure factors are used for further refinement. The random omit procedure is used to reduce model bias by deleting a small part of the structure and refining the rest. This is implemented differently in SHELXT due to the lack of a model at the P1 stage. The program determines the space group and origin shift by testing all possible space groups in the specified Laue group. The figure of merit α is used to evaluate the best solution. The chemical figure of merit CHEM is calculated by searching for bond angles and assigning elements based on integrated densities. The combined figure of merit CFOM is used to select the best solution. After assigning elements, an isotropic refinement is performed, followed by the determination of the Flack parameter and inversion of the structure if necessary. The structure is then built by clustering atoms and optimizing the position in the unit cell. Examples show SHELXT's effectiveness in solving various structures, including organoselenium compounds and pseudo-centrosymmetric structures. The program is available for free to academics and is suitable for multi-CPU computers. It has been tested on a large number of structures, with a high success rate in identifying the correct space group and element assignments. The program is recommended for use with caution, as incorrect element assignments can occur, especially in cases with disordered solvent molecules.