Your database can have contacts entered via many means, and duplicates can be accumulated.  Act! will check for you!
1.  Under your Tools menu, select Scan for Duplicates.  When you do so, a window will open allowing you to select the criteria scanned.  The Default is first Contact then Company.  If you wish, you can select other criteria, then select OK.  The program will run a check, and any duplicates will be listed.
2. Select 2 “matching” contact records from the list, then from the Tools menu, Copy/Move Data.  This will open a Wizard, where you select “Next”.  This will produce a list of fields in both records, where you can compare and select the BEST of the two records to save.  Select either Copy Contact 1 to Contact 2, or Copy Contact 2 to Contact 1, then Next.
3. In the screen showing in this step, you can select any Field Name on the left, then the Copy button near the top right.  This will copy the data from the middle list (Contact 1 in the first scenario, to Contact 2.)  Proceed through the list to transfer all desired data from one record to the other.  When you have finished the list, select Next.  The next window will allow you to select Notes, History, and other similar items to transfer.  Depending on your Act! version, this defaults to All or NOTHING!  I strongly suggest that you select all check boxes and thus transfer all Notes, etc, to the saved record.

Hit Next, and then Next again to delete one of the duplicate records…  and that’s it!

It is important to know that Act! recognizes EXACT duplicates:  It does not know Bob is Robert, or James is Jim!