This issue of Research in Mathematics Education (RME) marks a special point in the history of the journal. As incoming editors (beginning with volume 20), it is our honour to introduce volume 21 to celebrate 21 years of RME. As noted by the editors of volume 10 (Rowland & Nardi, 2008a), RME, an international journal with the explicit aim of being informative and relevant to researchers in the field world-wide, is the official journal of the British Society for Research into Learning Mathematics (BSRLM). Volume 10 coincided with the thirtieth anniversary of the formation of the British Society for the Psychology of Learning Mathematics (BSPLM), renamed BSRLM in 1985. The BSRLM spirit is at the heart of RME. Indeed, the editor of volume 1 (Brown, 1999, p. ii) of the journal wrote about being “excited by the ideas represented [in the first issue] and therefore discussed within the community of researchers and teachers which is BSRLM”. Likewise, the editors of volume 3 (Jones & Morgan, 2001, p. 3) drew attention to how the articles display interest in “a broad range of issues in mathematics education, making use of different theoretical frameworks and methodologies and including both reports of empirical studies and more theoretical contributions”. The early editions of the journal were published as single volumes (in effect, double issues). This changed with volume 10 when a pattern of two issues per year commenced. Two years later, in 2010, the journal editors (Nardi & Rowland, 2010) announced the journal’s growth to three issues per year, beginning with Volume 13. This established a pattern whereby Issues 1 and 3 of each volume are ‘regular’ issues and Issue 2 is a ‘Special Issue’ (SI) with guest editors. The first SI was entitled Deepening engagement in mathematics in pre-university education, with its introductory article (Wake, 2011) explaining how the SI reported on the outcomes of the TLRP project, a major funded UK research project (see: www.transmaths.org). Subsequent Special Issues, to date, have been entitled European research in mathematics education (Hodgen, Nardi, & Rowland, 2012), Experimental methods in mathematics education research (Alcock, Gilmore, & Inglis, 2013), Institutional, sociocultural and discursive approaches to research in university mathematics education (Nardi, Biza, González-Martín, Gueudet, & Winsløw, 2014), Mathematics teaching: Tales of the unexpected (Rowland, Hodgen, & Solomon, 2015), A discursive approach to the investigation of school mathematics (Morgan & Sfard, 2016), Summative Assessment (Iannone & Jones, 2017), and, most recently, Early Childhood Mathematics Education (Black & Norén, 2018). A feature introduced in Volume 18 was the occasional invited ‘position paper’ written by key researchers in mathematics education, and accompanying invited ‘response paper’ by a suitable respondent (see Hodgen, Simpson, & Solomon, 2016). The first such ‘position paper’ was by Julian Williams and Sophina Choudry (Williams & Choudry, 2016), and the response by Andy Noyes (2016). Subsequently, to date, a ‘position paper’ by Celia Hoyles (2018), with a response from Paul Drijvers (2018), appeared in Volume 20. As well as original research papers, RME has established a strong heritage of informed and critical book reviews, ably handled by the journal’s Book Reviews Editor. This heritage includes

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纪念数学教育研究 21 年

本期《数学教育研究》(RME) 标志着该期刊历史上的一个特殊点。作为即将到来的编辑（从第 20 卷开始），我们很荣幸推出第 21 卷来庆祝 RME 成立 21 周年。正如第 10 卷（Rowland & Nardi，2008a）的编辑所指出的，RME 是一份国际期刊，其明确目标是为全球该领域的研究人员提供信息和相关性，是英国研究协会的官方期刊学习数学（BSRLM）。第 10 卷恰逢英国数学学习心理学协会 (BSPLM) 成立三十周年，该协会于 1985 年更名为 BSRLM。BSRLM 精神是 RME 的核心。事实上，第 1 卷的编辑（Brown，1999，p. ii) 杂志写道，“被[第一期]所代表的想法所激发，因此在 BSRLM 的研究人员和教师社区内进行了讨论”。同样，第 3 卷（Jones & Morgan，2001，第 3 页）的编辑们提请注意这些文章如何对“数学教育中的广泛问题、利用不同的理论框架和方法并包括实证研究和更多的理论贡献”。该期刊的早期版本以单卷形式出版（实际上是双期）。当每年发行两期的模式开始时，这在第 10 卷中发生了变化。两年后，即 2010 年，期刊编辑 (Nardi & Rowland, 2010) 宣布该期刊从第 13 卷开始增加到每年三期。这建立了一种模式，即每卷的第 1 期和第 3 期是“常规”问题，而第 2 期是有客座编辑的“特刊”(SI)。第一个 SI 的标题是在大学预科教育中加深对数学的参与，其介绍性文章（Wake，2011 年）解释了 SI 如何报告 TLRP 项目的结果，这是一个主要资助的英国研究项目（参见：www.transmaths.组织）。迄今为止，后续特刊的标题为欧洲数学教育研究（Hodgen、Nardi 和 Rowland，2012 年）、数学教育研究中的实验方法（Alcock、Gilmore 和 Inglis，2013 年）、制度、社会文化和话语方法大学数学教育研究（Nardi、Biza、González-Martín、Gueudet 和 Winsløw，2014 年），数学教学：意想不到的故事（罗兰，Hodgen, & Solomon, 2015), 学校数学调查的话语方法 (Morgan & Sfard, 2016), 总结性评估 (Iannone & Jones, 2017)，以及最近的幼儿数学教育 (Black & Norén, 2018) ）。第 18 卷中引入的一个特点是偶尔邀请数学教育领域的主要研究人员撰写的“立场文件”，以及由合适的受访者撰写的邀请“回应文件”（参见 Hodgen、Simpson 和 Solomon，2016 年）。第一份这样的“立场文件”是 Julian Williams 和 Sophina Choudry（Williams & Choudry，2016 年）以及 Andy Noyes（2016 年）的回应。随后，迄今为止，西莉亚·霍伊斯 (Celia Hoyles) (2018) 的“立场文件”以及保罗·德里弗斯 (Paul Drijvers) (2018) 的回应出现在第 20 卷中。RME 在知情和批判性的书评方面建立了强大的传统，由期刊的书评编辑巧妙地处理。这份遗产包括