Here are some of the Proceedings of ICMI Study Conferences (preparatory conferences to ICMI Study books).
Already available are:
The Professional Education and Development of Teachers of Mathematics: Contributed Papers, Demonstrations and Worksessions.
Proceedings of the Study Conference for Study Number 16, Challenging Mathematics in and beyond the Classroom, which was held in Trondheim, Norway, from 28 June to 02 July 2006: Submitted Papers, Final Versions.
Proceedings of the Seventeenth ICMI Study Conference "Technology Revisited"
Hanoi University of Technology
December 3-8 2006
Edited by Celia Hoyles, Jean-Baptiste Lagrange, Le Hung Son and Nathalie Sinclair
Proceedings of the ICMI Study 18 Conference and IASE 2008 Round Table Conference (Joint ICMI/IASE Study Statistics in School Mathematics. Challenges for Teaching and Teacher Education). Editors: Carmen Batanero, Gail Burrill, Chris Reading and Allan Rossman. ISBN: 978-90-73592-28-5, 30 June- 4 July 2008, ITESM, Monterrey, Mexico.
Proceedings of the international Conference for ICMI Study 20, held in Lisbon, Portugal, on 11-15 October 2010 (the Proceedings are freely available in http://www.cim.pt/files/proceedings_eimi_2010.pdf). The international EIMI Study is a joint study between the International Commission on Mathematical Instruction (ICMI) of the International Mathematical Union and the ICIAM.
Proceedings of the international Conference for ICMI Study 22, Oxford, UK, July 2013. Task Design in Mathematics Education. Proceedings are online:
Proceedings of the international Conference for ICMI Study 23, Macau, China, June 2015. Primary Mathematics Study on Whole Numbers. Proceedings are online: www.umac.mo/fed/ICMI23/proceedings.html
Proceedings of the International Conference for ICMI Study 24, Tsukuba, Japan (November 2018) on curriculum reform are online.