How many references are needed?

We will usually expect a minimum of 20 references, primarily to journal papers  (25 references for each paper should be more common). Citations of textbooks and web pages should be used very rarely.  Also, references to conference papers are ignored when journals are ranked. Please be sure that you have current references (last couple of years). If there are no current references then there are two possibilities:

1. Authors are not following literature
2. There are not papers because other people are not interested in the subject

Both reasons are good enough for manuscript rejection.