This collection of papers provides an up to date treatment of item response theory, an important topic in educational testing.

1 The Life of Georg Rasch as a Mathematician and as a Statistician.- 2 The Growing Family of Rasch Models.- 3 Gain Scores Revisited Under an IRT Perspective.- 4 Modeling Learning in Short-Term Learning Tests.- 5 An IRT Model for Multiple Raters.- 6 Conditional Independence and Differential Item Functioning in the Two-Parameter Logistic Model.- 7 Differential Item Functioning Depending on General Covariates.- 8 Statistical Tests for Differential Test Functioning in Rasch's Model for Speed Tests.- 9 Expected Response Functions.- 10 A Logistic IRT Model for Decreasing and Increasing Item Characteristic Curves.- 11 Using Parameter Expansion to Improve the Performance of the EM Algorithm for Multidimensional IRT Population-Survey Models.- 12 Cross-Validating Item Parameter Estimation in Adaptive Testing.- 13 Imputation of Missing Scale Data with Item Response Models.- 14 On the Interplay Between Nonparametric and Parametric IRT, with Some Thoughts About the Future.- 15 Reversibility Revisited and Other Comparisons of Three Types of Polytomous IRT Models.- 16 Progress in NIRT Analysis of Polytomous Item Scores: Dilemmas and Practical Solutions.- 17 Two-Level Nonparametric Scaling for Dichotomous Data.- 18 The Circles of Our Minds: &A Nonparametric IRT Model for the Circumplex.- 19 Using Resampling Methods to Produce an Improved DIMTEST Procedure.- 20 Person Fit Across Subgroups: An Achievement Testing Example.- 21 Single-Peaked or Monotone Tracelines? On the Choice of an IRT Model for Scaling Data.- 22 Outline of a Faceted Theory of Item Response Data.- Abbreviations.