Teaching is a complex, ongoing endeavor that involves a myriad of decisions. NCTM's Sixty-Sixth Yearbook is organized around three aspects of teaching: foundations for teaching, the enactment of teaching, and the support of teaching nurtured in preservice education and strengthened throughout a teacher's career. The accompanying professional development guidebook, edited by George W. Bright, contains activities that illustrate and extend some of the ideas in the yearbook in order to further teachers' growth and development in understanding and implementing effective mathematics instruction. This yearbook divides into three parts and twenty-two chapters. Part One: "Foundations for Teaching," contains: (1) Equity in Mathematics Education Is about Access (Carol Malloy); (2) Developing a Well-Articulated Algebra Curriculum: Examples from the NCTM Academy for Professional Development (Jennifer M. Bay-Williams; Elizabeth M. Skipper; and Susan K. Eddins); (3) What Makes a Mathematical Task Worthwhile? Designing a Learning Tool for High School Mathematics Teachers (Fran Arbaugh and Catherine A. Brown); (4) Mathematical Foundations for a Functions-Based Approach to Algebra (M. Kathleen Heid; Rose Mary Zbiek; and Glendon W. Blume); and (5) Language Pitfalls and Pathways to Mathematics. (Carne Barnett-Clarke and Alma Ramirez). Part Two: "The Enactment of Teaching," contains: (6) Mathematics Teaching in Grades K-2: Painting a Picture of Challenging, Supportive, and Effective Classrooms (Barbara Clarke and Doug Clarke); (7) The NCTM "Standards" in a Japanese Primary School Classroom: Valuing Students' Diverse Ideas and Learning Paths (Aki Murata; Naoyuki Otani; Nobuaki Hattori; and Karen C. Fuson); (8) Beyond Presenting Good Problems: How a Japanese Teacher Implements a Mathematics Task (Margaret Smith); (9) Teaching to Develop Students as Learners (Debra I. Johanning and Teri Keusch); (10) Enlarging the Learning Community through Family Mathematics (Phyllis Whitin); (11) Building a Mathematical Community through Problem Posing (David J. Whitin); and (12) Promoting Equity in Mathematics Education through Effective, Culturally Responsive Teaching (Joan Cohen Jones). Part Three: "Support of Teaching," contains: (13) Enhancing the Mathematical Understanding of Prospective Teachers: Using Standards-Based, Grades K-12 Activities (Charlene E. Beckmann; Pamela J. Wells; John Gabrosek; Esther M. H. Billings; Edward F. Aboufadel; Phyllis Curtiss; William Dickinson; David Austin; and Alverna Champion); (14) Promoting Content Connections in Prospective Secondary School Teachers (Irene Bloom); (15) Facilitating Teachers' Growth in Content Knowledge (Kathleen Cramer); (16) Embracing the Complexity of Practice as a Site for Inquiry (Theresa J. Grand and Kate Kline); (17) The Reflective Teaching Model: A Professional Development Model for In-Service Mathematics Teachers (Lynn C. Hart; Deborah Najee-Ullah; and Karen Schultz); (18) Encouraging Professional Growth and Mathematics Reform through Collegial Interaction (P. Mark Taylor); (19) Developing a Support System for Teacher Change in Mathematics Education: The Principal's Role (Patricia A. Jaberg; Cheryl A. Lubinski; and Sigrid Aeschleman); (20) A Tool for the Teaching Principle: Professional Development "through" Assessment (Sandra Wilcox and Elizabeth M. Jones); (21) Teaching Mathematics with Technology: An Evidence-Based Road Map for the Journey (Karen Hollebrands and Rose Mary Zbiek); and (22) Teachers Teaching Teachers (Janet Warfield and Cheryl A. Lubinski).