The Excel VLOOKUP function 'looks up' a given value in the lefthand column of a data array (or table), and returns the corresponding value from another column of the array.
The syntax of the function is:
where the arguments are as follows:
lookup_value    The value that you want to look up.  
table_array    The data array or table, containing the search values in the left hand columns and the values to return in another column.  
col_index_num    The column number, within the supplied table_array, that you want to return a value from.  
[range_lookup]    An optional logical argument, that describes what the function should return in the event that it does not find an exact match to the lookup_value. The [range_lookup] can be set to TRUE or FALSE, meaning:  

Wildcards
In textrelated Vlookups, where an exact match is required, the lookup_value can contain the following wildcard characters:
?  matches any single character
*  matches any sequence of characters
In the spreadsheet below, columns A and B list an inventory of grocery items, and their prices, and cell E2 of the spreadsheet shows a simple example of the Vlookup function being used to look up the price of an item from the inventory.
A  B  C  D  E  

1  Item Description  Cost ($)  Current Item:  Current Item Cost ($)  
2  Tinned Tomatoes  $0.90  Cornflakes  =VLOOKUP( D2, A:B, 2, FALSE )   returns the value $3.50  
3  Tinned Tuna  $1.50  
4  Cornflakes  $3.50  
5  Shortcake Biscuits  $1.00  
6  Toothpaste  $4.10  
7  Tinned Baked Beans  $0.99  
8  White Sliced Bread  $0.80  
9  . . .  . . . 
The above Vlookup function returns the price for "Cornflakes", which is $3.50.
In this example:
In the spreadsheet below, columns AC list the grades that are assigned to examination marks lying within the ranges 044%, 45%54%, etc.
Cell F2 shows the score of 52% that was achieved by the student "Anne" in an examination. The Vlookup function in cell G2 looks up this score in column A of the spreadsheet and returns the associated grade from column C. Note that, in this example, if the exact score of 52% is not found in column A, we want, instead, to use the nearest value below this score.
A  B  C  D  E  F  G  

1  Lower  Upper  Grade  Name  Score  Grade  
2  0%  44%  F  Anne  52%  =VLOOKUP( F2, A2:C7, 3, TRUE )   returns the value "E"  
3  45%  54%  E  
4  55%  64%  D  
5  65%  74%  C  
6  75%  84%  B  
7  85%  100%  A 
The above Vlookup function returns the grade for the score 52%, which is E.
In this example:
For a practical example of the Vlookup function being used to create a variable chart, see the Excel Variable Chart page.
Also, there are several further Vlookup examples on the Microsoft Office website.
Although there is no VBA Vlookup function, you can call the Excel Worksheet Vlookup Function from VBA. See the VBA Vlookup page for more details.
If you get a Vlookup error this is likely to be one of the following:
#N/A    Occurs if the Vlookup function fails to find a match to the supplied lookup_value. The cause of this will generally depend on the supplied [range_lookup] argument:  
If you still can't understand why you are getting this Vlookup error, check out the Vlookup #N/A Error page.  
#REF!    Occurs if either:
If you need further help with this Vlookup error, check out the Vlookup #REF! Error page.  
#VALUE!    Occurs if either:
 
For further Vlookup troubleshooting tips, there is an excellent Quick Reference Card available on the Microsoft Office website 