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The term “predatory journals" was first coined by librarian Jeffrey Beall in 2012 to describe what he called “counterfeit journals". 
Predatory journals or publishers are now commonly referred as those that “actively solicit manuscripts and charge publication fees without providing robust peer review and editorial services.”
“There is no universally agreed definition of a predatory journal or publisher. However, organizations like the Committee on Publication Ethics (COPE) and the World Association of Medical Editors (WAME) define global publication ethics standards — predatory journals do not meet those standards.” -- Karen Holland, Prof. Peter Brimblecombe, Dr. Wim Meester and Susanne Steiginga,
The importance of high-quality content: curation and reevaluation in Scopus
Why is it important to identify them?
Devise strategies to deal with increased calls for papers/invitations to serve on editorial boards from unfamiliar sources and journals
Avoid potential loss of academic reputation/opportunities by being associated with poor-quality journals
Uphold high standards in publishing; poor-quality publications tarnish the credibility of academic literature
This guide was created to help answer the following questions, upon receiving an invitation from a publisher:
Should I publish my article in a particular journal?
Should I pay article processing charges to publish in an Open Access journal?
Should I edit a special issue for a particular journal?
Should I accept the invitation to serve on the editorial board of a particular journal?
Should I accept the invitation to be a keynote speaker at a particular conference?
Predatory Publishers on the Rise
Jeffrey Beall's numbers of predatory publishers from 2011 to 2016 show a dramatic increase.
Ayeni, P. O., & Adetoro, N. (2017). Growth of predatory open access journals: implication for quality assurance in library and information science research. Library Hi Tech News, 34(1), 17–22. https://doi.org/10.1108/LHTN-10-2016-0046
Developed by ASCE, Elsevier, IEEE and the IET, these guidelines aim to help maintain "an equitable balance of the interests of all participants in ensuring high quality, scholarly conference proceedings content."
Think. Check. Attend is an initiative that aims to guide and assist researchers and scholars to judge the legitimacy and academic credentials of conferences in order to help them decide whether to attend.