Introduction -- Does the Textbook Support the Implementation of Mathematical Problem-Posing in Classrooms? -- Problem Posing and Questioning -- Effective Factors and Beliefs About Mathematics of Chilean Young Children -- Reformulating: Mathematical Problem Solving as Inquiry -- Improving Mathematical Problem-Solving -- Reaction Paper.-Teaching Mathematical Problem Solving in Hungary for Students Who Have Average Ability in Maths -- Exploratory Problems as Propositions for Doing Mathematics -- On the Role of Corporeality, affect, and metaphoring in Problem Solving -- Building Thinking Classrooms: Conditions for Problem Solving -- Research Project Finland-Chile on Open Problem Solving in elementary Mathematics Teaching -- The Coordinated Use of Several Digital Technologies to Frame and Foster Learners' Mathematical Problem Solving Experiences -- Proportional Word Problem Solving Through a Modelling Lense -- Conceptual Model-Based Problem Solving -- Reaction Paper -- Novel Chilean Secondary Mathematics Teachers as Problem Solvers -- Infusing Mathematical Problem Solving in the Mathematics Curriculum -- Mathematical Problem Posing in Taiwan -- Mathematical Problem Solving and Teacher Professional Learning.