This work is focused at new Microsoft technology for querying data LINQ (Language intergrated query). It is built as complex technology, it allows working with various data sources. For example it contains collections of objects, created for temporary storing data in memory, but also data in robust database systems. In first part of this work I describe how data was queried before LINQ was on scene and what reasons made LINQ originate. Then I analyze new features in C# that were prerequisites for creating language integrated query as part of base libraries. Next part focuses at query operators, their interfaces and provides examples of use. Then I describe LINQ technology in complex, I create and describe in detail process of execution of LINQ query. Next chapter describes querying ADO.NET Datasets. Practical examples are created for both typed and untyped Datasets. In following chapter I analyze LINQ to SQL functionality. There is described method of implementation, mainly translation LINQ query to SQL language, integrated object rational mapping tool, change tracking in mapped objects including concurrency problems. At the end of the chapter I sketch the future in data access in ADO.NET entities. In last but one chapter is created complex application of use LINQ technology. Application is built as thin client that uses LINQ as for reading and manipulating data from relational database. In the application is LINQ also used common work with component that presents data. At the end part of this work is LINQ technology summarized. Contribution and pitfalls of LINQ technology are also described.