The International Reference Ionosphere (IRI) is a widely recognized and validated model that describes the ionosphere's monthly averages, including electron density, electron and ion temperatures, and ion composition. It represents variations in these parameters with altitude, latitude, longitude, date, and time, influenced by external factors such as solar indices, ionospheric indices, and magnetic indices. IRI also provides additional output parameters like vertical ionospheric total electron content (vIITEC). IRI is synthesized from almost all available and reliable ionospheric data, making it a recognized standard by organizations like COSPAR, URSI, ITU, ECCS, and ISO. It continues to improve with new data and includes effects not yet fully explained by theory. However, it has limitations, such as a bias towards Northern mid-latitudes and data-sparse regions requiring interpolation. Recent improvements include new options for hmF2, such as Altadill et al. (2013) and Shubin (2015), which enhance the model's fit to observations. Truhlik et al. (2013) improved ion composition at high and low solar activity levels. IRTAM (IRI Real-Time Assimilative Mapping) by Galkin et al. (2012) uses ionosonde data from the Global Ionosphere Radio Observatory (GIRO) network to provide real-time updates. IRI is extensively used in scientific publications, particularly in AGU journals like JGR, GRL, RS, and SW. Regular workshops and publications are held to discuss and advance the model, with recent topics including data assimilation, equatorial latitudes, and ionospheric weather predictions.The International Reference Ionosphere (IRI) is a widely recognized and validated model that describes the ionosphere's monthly averages, including electron density, electron and ion temperatures, and ion composition. It represents variations in these parameters with altitude, latitude, longitude, date, and time, influenced by external factors such as solar indices, ionospheric indices, and magnetic indices. IRI also provides additional output parameters like vertical ionospheric total electron content (vIITEC). IRI is synthesized from almost all available and reliable ionospheric data, making it a recognized standard by organizations like COSPAR, URSI, ITU, ECCS, and ISO. It continues to improve with new data and includes effects not yet fully explained by theory. However, it has limitations, such as a bias towards Northern mid-latitudes and data-sparse regions requiring interpolation. Recent improvements include new options for hmF2, such as Altadill et al. (2013) and Shubin (2015), which enhance the model's fit to observations. Truhlik et al. (2013) improved ion composition at high and low solar activity levels. IRTAM (IRI Real-Time Assimilative Mapping) by Galkin et al. (2012) uses ionosonde data from the Global Ionosphere Radio Observatory (GIRO) network to provide real-time updates. IRI is extensively used in scientific publications, particularly in AGU journals like JGR, GRL, RS, and SW. Regular workshops and publications are held to discuss and advance the model, with recent topics including data assimilation, equatorial latitudes, and ionospheric weather predictions.