The Delphi Survey technique is a popular method used in foresight and other futures studies. It involves a panel of experts that judge the timing, probability, importance and implications of factors, trends, and events regarding the problem in question. 
There are eight steps to the Delphi method:
- The specification of some topic or subject whose possible, probable, and preferable futures are to be investigated.
- The construction of a questionnaire as an instrument of data collection.
- The selection of some individuals (respondents) whose opinions are to be studied, usually experts on the topic.
- The initial measurement of the opinions of the respondents by means of a questionnaire.
- The preliminary organisation and summary of the data resulting from the initial measurement.
- The communication of the results of the initial measurement of opinions as feedback to all the respondents.
- A re-measurement of the opinions of the respondents as they have been informed and may have been changed by their knowledge of earlier results including those of other respondents supporting comments for their opinions.
- An analysis, interpretation and presentation of the data and the writing of the final report.
The basic idea of the Delphi method is as follows:
- create a list of statements/questions
- have the experts give their ratings/answers/etc.
- make a report - send it out to everyone
- have the experts revise their answers
- make the second report
You now have the best "answers" that current expert knoweldge allows. The methodology for Delphi (how to carry out every step) is well developed and the method is used a lot. In particular it is used in technology foresight, which is the most successful future predicting methodology.