Citizen science is one of the most dramatic developments in science communication in the last generation. But analyses of citizen science, of what it means for science and especially for science communication, have just begun to appear. Articles in this first of two special issues of JCOM address three intertwined concerns in this emerging field: The motivation of citizen science participants, the relationship of citizen science with education, and the implications of participation for creation of democratic engagement in science-linked issues. Ultimately these articles contribute to answering the core question: What does citizen science mean?

Citizen Science is part of a broader reconfiguration of the relationship between science and the public in the digital age: Knowledge production and the reception of scientific knowledge are becoming increasingly socially inclusive. We argue that the digital revolution brings the "problem of extension" — identified by Collins and Evans in the context of science and technology governance — now closer to the core of scientific practice. In order to grasp the implications of the inclusion of non-experts in science, the aim of this contribution is to define a role-set of non-certified knowledge production and reception, serving as a heuristic instrument for empirical clarifications.

Success stories of citizen science projects widely demonstrate the value of this open science paradigm and encourage organizations to shift towards new ways of doing research. While benefits for researchers are clear, outcomes for individuals participating in these projects are not easy to assess. The wide spectrum of volunteers collaborating in citizen science projects greatly contributes to the difficulty in the evaluation of the projects' outcomes. Given the strong links between many citizen science projects and education, in this work we present an experience with hundreds of students (aged 15–18) of two different countries who participate in a project on cell biology research — Cell Spotting — as part of their regular classroom activities. Apart from introducing the project and resources involved, we aim to provide an overview of the benefits of integrating citizen science in the context of formal science education and of what teachers and students may obtain from it. In this case, besides helping students to consolidate and apply theoretical concepts included in the school curriculum, some other types of informal learning have also been observed such as the feeling of playing a key role, which contributed to an increase of students' motivation.

Since 2009 Vetenskap & Allmänhet (Public & Science, VA) coordinates an annual mass experiment as part of ForskarFredag — the Swedish events on the European Researchers' Night. Through the experiments, thousands of Swedish students from preschool to upper secondary school have contributed to the development of scientific knowledge on, for example, the acoustic environment in classrooms, children's and adolescents' perception of hazardous environments and the development of autumn leaves in deciduous trees. The aim is to stimulate scientific literacy and an interest in science while generating scientific output. The essay discusses how the mass experiments can contribute to encouraging scientific citizenship.

Open Science may become the next scientific revolution, but still lingers in a pre-paradigmatic phase, characterised by the lack of established definitions and domains. Certainly, Open Science requires a new vision of the way to produce and share scientific knowledge, as well as new skills. Therefore, education plays a crucial role in supporting this cultural change along the path of science. This is the basic principle inspiring the collection of essays published in this issue of JCOM, which deals with many subjects ranging from open access to the public engagement in scientific research, from open data to the social function of preprint servers for the physicians' community. These are issues that go along with the targets of the FOSTER project (Facilitate Open Science Training for European Research) funded by the European Union, which has provided interesting food for thought in order to write this commentary.

A hybrid combination of art and science is used to communicate science in a primary school setting. The purpose of the work is to enhance student awareness of the science behind understanding the global climate system with a focus on the cryosphere. An experiment in communicating science is conducted by taking the collaborative experiences of a professional artist and scientist, which are then combined and projected onto an ostensibly everyday primary school classroom project. The tangible end result is a stand-alone contemporary art work that then is the focal point of community-based promotion of the science and creativity involved. A range of qualitative evaluation elements suggest that the approach does improve student engagement with the scientific approach and reduces the student's uncertainty about ``what science is''.

Teaching mathematics in informal settings is a relatively new phenomenon, but it has gained more attention due to the recent changes in the society. The aim of the present quantitative study was to compare the learning outcomes of Latvian and Swedish 12-year-olds when they visited a science centre mathematics-art exhibition originally designed in Estonia. The results showed that in general, prior knowledge of the exhibition contents was the strongest predictor of post-test results in both countries but that mathematical thinking skills and self-concept had a small added value in explaining the post-test results. The results of the study give some of the first pieces of evidence of the effectiveness of out-of-school mathematics teaching in a science exhibition context, providing a good basis for further studies.

The design, delivery and evaluation of JCOM Masterclasses has given us the opportunity to reflect on the audiences, training needs and training schemes available to people working at different levels and in different contexts to communicate STEM subjects to a diverse variety of people. Although not always widely available, short courses in the communication of science have been offered in a number of countries around the world over the past few years. We felt it is now time to open a discussion on the rationale, the methods and the objectives of such training programmes.

This study addresses an open question about science bloggers' self-perceived roles as science communicators. Previous research has investigated the roles science journalists see themselves engaging in, but such research has failed to capture the experiences of science bloggers as a broad and diverse group that is yet often very different in their practices from professional journalists. In this study, a survey of over 600 science bloggers reveals that on the broadest level, science bloggers see themselves engaging most often as explainers of science and public intellectuals. Perceived communication role depends predominantly on occupation, science communication training, blog affiliation and gender.

The ever-changing nature of academic science communication discourse can make it challenging for those not intimately associated with the field ― scientists and science-communication practitioners or new-comers to the field such as graduate students ― to keep up with the research. This collection of articles provides a comprehensive overview of the subject and serves as a thorough reference book for students and practitioners of science communication.