InhaltsangabeGrounding Mathematics Education.- Sign Processes.- Agency and Creativity in the Semiotics of Learning Mathematics.- The Semiotic Approach to Mathematical Evidence and Generalization.- Signs as Means for Discoveries.- Diagrammatic Thinking.- Notes on a Semiotically Inspired Theory of Teaching and Learning.- Mathematics, Sign and Activity.- Sign Processes in the Mathematics Classroom.- Semiotic Mediation in the Primary School.- Do Mathematical Symbols Serve to Describe or Construct "Reality"?.- Metaphor and Metonymy in Processes of Semiosis in Mathematics Education.- On Practical and Theoretical Thinking and Other False Dichotomies in Mathematics Education.- The Semiotics of the Schema.- Mathematics Education as a Science.- Towards a Normal Science of Mathematics Education?.- The Study of the Didactical Conditions of School Learning in Mathematics.- The Formal, The Social and the Subjective.- Crossing Boundaries.- Reflective Learning.- Thinking and Knowing About Knowledge.- The Cognitive Unconscious.- History of Mathematics and Mathematics Education.- Hilbert, Weyl, and the Philosophy of Mathematics.- Mathematical Metaphors in Natorp's Neo-Kantian Epistemology and Philosophy of Science.- Newton's Program of Mathematizing Nature.- Did Hermann and Robert Graßmann Contribute to the Emergence of Formal Axiomatics?.- A Case Study in Generalisation.- Some German Contributions to Mathematics Research in Brazil.- Making Philosophy of Mathematics Relevant.- Data Structures and Virtual Worlds.- Variables, in Particular Random Variables.- Deduction, Perception, and Modeling.- Models of Data, Theoretical Models, and Ontology.- Some Sober Conceptions of Mathematical Truth.- Can There Be an Alternative Mathematics, Really?.- Coda.- An Interview with Michael Otte.