The new Hipparcos astrometric reduction, published by van Leeuwen, claims improved accuracy for stars brighter than magnitude H_p = 8, up to a factor of 4 better than the original 1997 catalogue. The paper validates the new reduction by checking data quality, formal errors, and error correlations. It explains differences between the new and old reductions. The new reduction improves the total weight of the data by a factor of 2.2 compared to the 1997 catalogue, providing better data for stellar luminosity and galactic kinematics studies. The new reduction addresses issues in the original, such as inaccuracies in the along-scan attitude reconstruction. It uses a global iterative solution instead of the previous great-circle method, improving attitude reconstruction and allowing for better control. The new reduction also improves the connectivity requirement in the along-scan attitude reconstruction, enabling sufficient contributions from both fields of view to avoid local distortions. The new reduction improves the accuracy of the Hipparcos data by better understanding the noise sources, including photon noise and attitude noise. The formal errors on the parallaxes are confirmed, with the new reduction showing a significant improvement in accuracy. The new reduction also improves the correlation levels of the abscissa residuals, reducing the impact of correlated errors. The new reduction also improves the basic angle and other instrument parameters, leading to more accurate geometric distortions. The new reduction uses a fully-dynamic model for the along-scan attitude, allowing for better reconstruction of the satellite's attitude and reducing the impact of errors. The new reduction also improves the field-of-view transits and astrometric parameters, leading to more accurate astrometric solutions. The new reduction reduces the attitude noise, leading to smaller formal errors on the astrometric parameters. The new reduction also improves the correlation levels of the abscissa residuals, reducing the impact of correlated errors. The new reduction also improves the formal errors and their dependencies, leading to more accurate astrometric solutions. The new reduction reduces the correlation levels of the abscissa residuals, reducing the impact of correlated errors. The new reduction also improves the special cases of stars in the Hipparcos catalogue, providing more accurate astrometric solutions for these stars. The new reduction is validated by comparing it with radio-star observations, showing good agreement between the new reduction and the 1997 catalogue. The new reduction also shows good agreement with the ICRS, with small differential rotations between the two catalogues. The new reduction also shows improved accuracy in the parallaxes, with a smaller number of negative parallaxes and better formal errors. The new reduction provides a more accurate and reliable astrometric data set for the Hipparcos mission, with significant improvements in accuracy and data quality. The new reduction is a major improvement over the original 1997 catalogue, providing better data for a wide range of stellar studies.The new Hipparcos astrometric reduction, published by van Leeuwen, claims improved accuracy for stars brighter than magnitude H_p = 8, up to a factor of 4 better than the original 1997 catalogue. The paper validates the new reduction by checking data quality, formal errors, and error correlations. It explains differences between the new and old reductions. The new reduction improves the total weight of the data by a factor of 2.2 compared to the 1997 catalogue, providing better data for stellar luminosity and galactic kinematics studies. The new reduction addresses issues in the original, such as inaccuracies in the along-scan attitude reconstruction. It uses a global iterative solution instead of the previous great-circle method, improving attitude reconstruction and allowing for better control. The new reduction also improves the connectivity requirement in the along-scan attitude reconstruction, enabling sufficient contributions from both fields of view to avoid local distortions. The new reduction improves the accuracy of the Hipparcos data by better understanding the noise sources, including photon noise and attitude noise. The formal errors on the parallaxes are confirmed, with the new reduction showing a significant improvement in accuracy. The new reduction also improves the correlation levels of the abscissa residuals, reducing the impact of correlated errors. The new reduction also improves the basic angle and other instrument parameters, leading to more accurate geometric distortions. The new reduction uses a fully-dynamic model for the along-scan attitude, allowing for better reconstruction of the satellite's attitude and reducing the impact of errors. The new reduction also improves the field-of-view transits and astrometric parameters, leading to more accurate astrometric solutions. The new reduction reduces the attitude noise, leading to smaller formal errors on the astrometric parameters. The new reduction also improves the correlation levels of the abscissa residuals, reducing the impact of correlated errors. The new reduction also improves the formal errors and their dependencies, leading to more accurate astrometric solutions. The new reduction reduces the correlation levels of the abscissa residuals, reducing the impact of correlated errors. The new reduction also improves the special cases of stars in the Hipparcos catalogue, providing more accurate astrometric solutions for these stars. The new reduction is validated by comparing it with radio-star observations, showing good agreement between the new reduction and the 1997 catalogue. The new reduction also shows good agreement with the ICRS, with small differential rotations between the two catalogues. The new reduction also shows improved accuracy in the parallaxes, with a smaller number of negative parallaxes and better formal errors. The new reduction provides a more accurate and reliable astrometric data set for the Hipparcos mission, with significant improvements in accuracy and data quality. The new reduction is a major improvement over the original 1997 catalogue, providing better data for a wide range of stellar studies.