If you are a website programmer, you are developing applications that are multi-threaded (whether you know it or not!). This is wonderful and wicked at the same time. Why, do you ask?  Many different users can request the same page with the same options, causing the same code paths to be taken. Suppose you have a collection that needs to be shared across all users within your website. Using the code from the article A New Approach to HttpRuntime.Cache Management, you can certainly store a collection like this in a thread safe manner in HttpRuntime cache. Or, perhaps you can use the Singleton pattern to ensure a single collection. Loading that collection is another matter completely.