We were recently asked how to produce a report that lists Opportunities with no Activities linked to them. Please see below how to create this report.

• Create a new report, based on Opportunities. The quickest and easiest way to do this is to click Start > New > Report, select 'A new prepopulated report' and then select Opportunities as the record type from which to create the report.
• Add in the columns you require (and we recommend including a column for Object Reference, which you should call Opportunity Object Reference).
• Add in columns to join your Opportunities to Activities, by clicking Add column, selecting Activities and then using the dropdown picklist to select the fields you want on your report. Again, we recommend including the Object Reference for the Activity and calling the column Activity Object Reference.
• Add a Summary view to your report. Click Add value column and select the Summarised column option to generate a dialogue box like the one shown below (click to enlarge):

The Column field has been populated with the Activity Object Reference from the Details view of the report and I've used the Calculate field to specify that I want the report to count the number of Activity Object References that are in the Details view. I've then used the Opportunity Object Reference to group the data in the Summary view into one row for each Opportunity. Once you click Save & Close and look at a preview of your report, the output will look something like this:

So now you have a summary view that shows you how many Activities have been linked to each Opportunity and you can easily apply a calculated criteria to just return those Opportunities which do not have any Activities linked to them. Of course, you can apply criteria to your report to restrict the results to just open Opportunities, Activities of a specific type and so on.