I know this is a well trodden path but I am confused. I need to
connect an Access 2010 database to a SQL Server. I make two different
connections:

1 linking a table:
Dim aTable as DAO.TableDef
....
aTable.connect = aConnectionString

2 a ADODB connection
Dim theConnection As ADODB.Connection
Set theConnection = New ADODB.Connection
theConnection.Open theConnectionString

I am content with most of each connection string but am confused about
user id and password. Sometimes I seem to need:
UID= username; PWD= password

and at others:
User ID = username; Password = password

Can someone please explain when to use one form and when to use the
other.

I promise to note it down and remember it for future use.

Jim Devenish wrote:
That's the old ODBC syntax - use it when you are using ODBC, such as with
DAO connections and with linked tables.

is that there is an OLE DB provider for ODBC databases (it's called
MSDASQL). This provider is used when you need to use ADO to communicate via
an ODBC driver. It's not really recommended since you are forcing there to
be an extra layer of software between your code and the database: code->OLE
DB->ODBC->database. When using ADO to communicate with a database for which
a native OLE DB provider exists (such as SQL Server) it is preferable to use
the native OLE DB provider (SQLOLEDB for SQL Server).
When using a native provider, the OLE DB syntax should be used.
It seems that when using this MSDASQL provider, either syntax is acceptable.
I tend to use the UID/PWD syntax whenever I'm using ODBC, whether I'm using
ADO or not, but that's a matter of preference.

.... or just refer to www.connectionstrings.com ...