The following list is a collection of useful articles from two great resources, MSDN Library and the Knowledge Base. The list is updated on a regular basis.

Office Developer How-to Center
This is the portal for all How-to articles Microsoft publish and it cover Office 2007 together with Microsoft Office SharePoint Server:

• How-to Center

Excel 2007
For various reasons I have decided to single out articles that explicit only targeting Excel 2007 from both MSDN and Knowledge Base:

General

• 2007 Office System: Developer Posters
• Walkthrough: Deploying a Document and an Assembly to a Local Folder
• Improving performance in Excel 2007 (written by Charles Williams)
• 2007 Office System Sample: Visual Studio Code Snippets for the Office Fluent UI

Security

• 2007 Microsoft Office Security Guide
• Security policies and settings in the 2007 Office system

Office Open XML Formats

• OpenXML Developer
• XML in Office Developer Portal
• Open XML Formats Resource Center
• Open XML Format SDK 1.0
• Welcome to the Open XML Format SDK 1.0
• Manipulating Excel 2007 and PowerPoint 2007 Files with the Open XML Object Model (Part 1 of 2)
• Manipulating Excel 2007 and PowerPoint 2007 Files with the Open XML Object Model (Part 2 of 2)
• 2007 Office System: XML Schema Reference
• Retrieving Excel 2007 cell values
• Retrieving Lists of Excel 2007 Worksheets

Ribbon

• Ribbon
• Developer Overview of the User Interface for the 2007 Microsoft Office System
• 2007 Office System Document: UI Style Guide for Solutions and Add-ins
• Customizing the Office (2007) Ribbon User Interface for Developers (Part 1 of 3)
• Customizing the Office (2007) Ribbon User Interface for Developers (Part 2 of 3)
• Customizing the Office (2007) Ribbon User Interface for Developers (Part 3 of 3)
• Programmatically Customizing the Office 2007 Fluent User Interface

Add-ins

• Microsoft SQL Server 2005 Data Mining Add-ins for Microsoft Office 2007
  Data Mining Add-ins for Office 2007 readme
  Introducing the SQL Server 2005 Data Mining Add-ins for Office 2007
• Excel 2007 Document: Designing SQL Server 2005 Analysis Services Cubes for Excel 2007 Pivottables
• 2007 Microsoft Office Add-in: Microsoft Save As PDF for XPS
• Developing Add-ins (XLLs) in Excel 2007 (written by Steve Dalton)
COM Add-in unloads before the application is shut down in Microsoft Excel 
(It also apply to previously versions of Excel)
Developing User-Defined Functions for Excel 2007 and Excel Services
Excel 2007 XLL Software Development Kit
Excel 2007 XLL Software Development Kit Documentation (online version)

Tools

• Custom UI Tool (for the Ribbon UI)
• 2007 Office System Driver: Data Connectivity Components

Hotfixes

• Description of the Excel 2007 hotfix package: October 9, 2007

Excel

Advanced COM Interop

• Advanced COM Interoperability for VS 2003
• Advanced COM Interoperability for VS 2005
• Advanced COM Interoperability for VS 2008

Office Integration

• Office Integration

Running Multiply Version of Office on the same computer

• Office 2007
• Office 2003
• Office XP
• Office 2000

Server Side Automation of Office
This is also an area I've decided to view in a similar way as with articles for Excel 2007.

• Considerations for server-side Automation of Office

Office and WebServices

• Office and WebServices

MSDN Library

Excel & VBA

• Microsoft Excel 2000 Object Model
• Microsoft Excel XP Object Model
• Working with Microsoft Excel Objects
• Getting the Most Out of Visual Basic for Applications
• Working with Shared Office Components
• Using Ranges
• EXCELlent Office Adventures
• EXCELlent Office Adventures, Part 2
• Programming the Microsoft Office Visual Basic Editor
• Office VBA and the Windows API
• Working with Files, Folders, and Drives: More VBA Tips and Tricks
• Working with Strings and Dates: VBA Tips and Tricks
• Ten Code Conversions for VBA, Visual Basic .NET, and C#
• Using the SearchFolders Collection
• Ten Tips for Microsoft Office VBA Library Development
• New Toolkit Lets You Share Information Between Office Documents and Web Services
• Enhance Your Apps with Common Dialogs: Part I
• Understanding Optimization

VB.NET and Excel

• Handling Complex COM objects with Interop Assemblies
• Accessing Microsoft Office Data from .NET Applications
• Garbage Collector Basic and Performance Hints
• Bring the Power of Visual Studio.NET to Business Solutions Built with Microsoft Office
• Microsoft .NET Development for Microsoft Office - Basics of Office Interoperabilit Part 1
• Microsoft .NET Development for Microsoft Office - Basics of Office Interoperabilit Part 2
• Microsoft .NET Development for Microsoft Office - Basics of Office Interoperabilit Part 3
• Working with the Office XP Primary Interop Assemblies
• How To: Install Primary Interop Assemblies

Add-ins 

• Excel Add-ins
• Add-ins, Templates, Wizards, and Libraries
• Deployment of Managed COM Add-Ins in Office XP
• Secure Deployment of Managed COM Add-Ins in Office XP 
• Using the COM Add-in Shim Solution to Deploy Managed COM Add-ins in Office XP
• Building a COM Add-in for Microsoft Office XP Using Microsoft Visual Basic 6.0
• Microsoft Office Development with Visual Studio
• A Primer to the Office XP Primary Interop Assemblies
• Tips and Tricks: Building Microsoft Office Add-ins with Visual C# .NET and Visual Basic .NET
• How to enable or to disable the instantiation point of a specific COM category in an Office 2003 Service Pack 3 program

Calculation Engine

• Recalculation in Microsoft Excel 2002

DDE - Dynamic Data Exchange

• DDE Function

Help

• HTML Help Start Page
• Displaying Custom Help Topics in an Office Application's Help Window

XML

• XML Spreadsheet Reference
• Transfer XML Data to Microsoft Office Excel 2003 with Microsoft Visual Basic .NET
• Using the Excel 2003 Object Model to Add XML Data Integration
• Using the XML Features of Excel 2003 Object Model
• Automating the XML Data Mapping Process in Excel 2003
• Mapping XML from SQL Server to a single cell in Excel 2003
• Replicating Excel 2003 Formulas to SQL Server
• Add XML Functionality in Microsoft Excel 2003 from Microsoft Visual Basic.NET

Knowledge Base

• Q153307 - Call Microsoft Excel Macros That Take Parameters
• Q162059 - How to Configure Internet Explorer to Open Office Documents in the Appropriate Office program instead of Internet Explorer
• Q163435 - Programming Resources for Visual Basic for Applications 97
• Q165518 - Calling Macros Using OLE from MS Visual Basic for Applicatons
• Q167909 - Securing Visual Basic Code in Microsoft Excel
• Q223789 - How to minimize metadata in Microsoft Excel Workbooks
• Q226118 - Programming Resources for Visual Basic for Applications 2000
• Q240150 - Use Excel Startup Folders in Excel 2000
• Q244167 - Writing Automation Clients for Multiple Office Versions
• Q245115 - Using Early Binding and Late Binding in Automation
• Q259926 - How to Use Excel Startup Folders
• Q288902 - GetObject and CreateObject Behavior of Office Automation Servers
• Q291057 - Methods for Recovering Data from Damaged Workbooks
• Q291218 - Use Excel Startup Folders in Excel 2002
• Q291288 - Description of the startup switches for Excel
• Q291392 - Excel COM Add-ins and Automation Add-ins
• Q305326 - Programming Resources for Visual Basic for Applications XP
• Q829070 - How to use Visual Basic for Applications (VBA) to change UserForms in Excel 2003, Excel 2002, and Excel 2000
• Q817248 - How to call a Visual Basic.NET or Visual Basic 2005 assembly from Visual Basic 6.0
• Information about certain file types that are blocked after you install Office 2003 Service Pack 3

Add-ins

• Q108425 - How to Create Add-in Application Name and Description
• Q142120 - How to Create an Add-in
• Q151490 - How to Create a Global User-Defined Function
• Q152152 - Generic XLL Template
• Q161439 - How to Remove Entries from Add-Ins Dialog Box
• Q178474 - Build an Add-in (XLL) for Excel Using Visual C++
• Q213439 - Add-Ins Don't Load When Using the CreateObject Command
• Q214298 - Create an Add-in Application Name and Description in Excel 2000
• Q238228 - Build an Office 2000 COM Add-In in Visual Basic
• Q256624 - Use a COM Add-In Function as an Excel Worksheet Function
• Q278328 - How to Mark an Automation Add-in Function as Volatile
• Q280290 - Install an Excel Add-In (XLA or XLL) with Automation
• Q285337 - Create a Visual Basic Automation Add-in for Excel 2002 Worksheet Functions
• Q290868 - How to configure an Office COM Add-in for all users on a system
• Q291392 - Excel COM Add-ins and Automation Add-ins
• Q302896 - Build an Office COM Add-in by Using Visual Basic .NET
• Q303871 - Create an Excel Macro by Using Automation from Visual Basic .NET
• Information about designing Office XP add-ins and Office 2003 add-ins by using the .NET Framework

Pivottable & MS Query

• Q104308 - Optimizing PivotTable Performance
• Q114150 - Query to Find Unmatched Records Between Two Files
• Q136699 - Description and Usage of Joins in Microsoft Query
• Q162476 - Purpose of the PivotTable Optimize Memory Option
• Q180599 - How to Use MS Query to Merge Two Excel Files for a Mail Merge Data Source
• Q211515 - Using Server Page Fields in PivotTables
• Q211517 - Limits of PivotTables in Microsoft Excel

Webboffice Components

• Q235883 - Use the Spreadsheet Web Component with Visual Basic
• Q235885 - Use the Chart Web Component with Visual Basic
• Q248822 - Use Custom Functions with the Spreadsheet Component
• Q278976 - Use XSL to Transform Excel XML Spreadsheet for Server-Side Use
• Q288130 - Use ASP to Build Spreadsheet XML for Client-Side Display
• Q288215 - Microsoft Excel 2002 and XML
• Q288729 - General Information About Licensing and Using Office XP Web Components
• Q288732 - Deploy the Office XP Web Components in an Office Program
• Q830138 - The OLAP PivotTable Consideration

Excel & Classic VB / VB.NET

• Q142357 - Visual Basic Example Using BuildSQL
• Q194611 - Create and Call an Excel Macro Programmatically from VB
• Q214388 - How to run multiple versions of Excel on the same computer
• Q219151 - Automate Microsoft Excel from Visual Basic
• Q219905 - Dynamically Add and Run a VBA Macro from Visual Basic
• Q247412 - Methods for Transferring Data to Excel from Visual Basic
• Q284876 - Bug: Excel Fails when Automation Add-in Loads
• Q301982 - Automate Microsoft Excel from Visual Basic .NET
• Q302094 - Automate Excel From Visual Basic .Net To Fill or Obtain Data In a Range Using Arrays
• Q302814 - Handle Events for Excel by Using Visual Basic .NET
• Q302896 - How To build an Office COM add-in by Using Visual Basic.NET
• Q303017 - Use Automation to Create Office Command Bars and Controls with Visual Basic.NET
• Q303294 - Use Automation to Get and Set Office Document Properties with Visual Basic .NET
• Q306022 - Transfer Data to an Excel Workbook by Using Visual Basic .NET
• Q311452 - Develop Microsoft Office Solutions with Visual Studio .NET
• Q311731 - Query and Display Excel Data by Using ASP.NET, ADO.NET and Visual Basic .NET
• Q315731 - Retrieve the Names of Macros from an Excel Workbook by Using Visual Basic 6.0
• Q316831 - You cannot configure data connection to Excel files in Visual Studio .NET
• Q316934 - Use ADO.NET to Retrieve and Modify Records in an Excel Workbook With Visual Basic.NET
• Q317535 - How to Call a Visual Basic.NET Class Library from Visual Basic Application in Microsoft Office.
• Q318373 - Retrieve Metadata from Excel by Using the GetOleDbSchemaTable Method in Visual Basic.NET
• Q319180 - Transform a DataSet to Spreadsheet XML for Excel by Using Visual Basic .NET and ASP.NET
• Q320399 - Bug: "Old Format or invalid type library" error when automating Excel 
• Q830033 - How to apply Windows XP themes to Office COM Add-ins
• Q830761 - Best practises for deploying Visual Basic 6.0 applications
• Q840585 - Information about designing Office XP add-ins and Office 2003 add-ins by using the .NET Framework

Excel & DAO / ADO

• Q129856 - Use DAO GetRows Method to Fill Variant Arrays
• Q139402 - How to Use DAO to Create a New Microsoft Excel Workbook
• Q141686 - How to Use DAO to Append the Records in Two Tables
• Q141687 - How to Find Unmatched Records Between Tables Using DAO
• Q146406 - How to Retrieve a Table from Access into Excel Using DAO
• Q146607 - How To Retrieve the Results of a Parameter Query Using DAO
• Q149254 - How to Return DAO Query Results Directly to a List Box
• Q167957 - Extracting Error Information from ADO in VB
• Q168335 - Using ActiveX Data Objects (ADO) via Visual Basic
• Q168336 - How to Open ADO Connection and Recordset Objects
• Q168354 - Underlying OLE and OLEDB Provider Errors Are Exposed Through ADO
• Q190195 - Extract Information from Excel Sheet with DAO
• Q214289 - Overview of ODBC Add-in Functions and Arguments
• Q244761 - How to Use ADO to Return Data to a ListBox or ComboBox
• Q246335 - Transfer Data from an ADO Recordset to Excel with Automation
• Q247412 - Methods for Transferring data to Excel from Visual Basic
• Q257819 - Use ADO with Excel Data from Visual Basic or VBA
• Q278973 - ExcelADO Demonstrates How to Use ADO to Read and Write Data in Excel Workbooks
• Q282852 - An Overview of Data Tables in Microsoft Excel
• Q295646 - Transfer Data from ADO Data Source to Excel with ADO
• Q303814 - Use ADOX with Excel Data from Visual Basic or VBA
• Q319998 - Memory leaks occurs when tyou query an open Excel worksheet by using ActiveX Data Objects (ADO)         Important!
• Q321686 - Import Data into SQL Server from Excel

Office Automation

• Q167223 - OFF97: Microsoft Office 97 Automation Help File Available
• Q260410 - OFF2000: Microsoft Office 2000 Automation Help File Available
• Q302460 - OFFXP: Microsoft Office XP Automation Help File Available
• Q238984 - Improving the Performance of Office Automation Code
• Q292491 - Office Automation When Multiple Versions of Office Are Installed
• Q244167 - Writing Automation Clients for Multiple Office Versions

Windows API

• Use the Registry API to Save and Retrieve Setting

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