Medical interventions produce a broad range of data types: text-based data, for example a physician's notes describing the patient encounter; physiological signals such as the well known electrocardiogram (ECG), but also recordings from brain (electroencephalogram, EEG) and muscle activity (electromyogram, EMG); and images such as Compute Tomography (CT) scans, Magnetic Resonance Images (MRI) or ultrasound images. In addition, recent progress in medical science and technology has led to the accumulation of a tremendous amount of genomic data in support of individualised healthcare and personalised therapies. In this section, the characteristics of typical clinical data are introduced, followed by a brief introduction to genomic data. Coding of data is important for summarising data in computer systems. Well known examples are Read Codes and SNOMED-CT. These assist in promoting a shared understanding for the healthcare professionals and facilitate the use of software tools for medical audit, classification and research. Interoperability, which allows computer systems to communicate, is an important concept. Unambiguous description and standards are important. Web standards based on XML, facilitate WEB2.0 participation, with a view to producing a semantic web. For health, we provide an example based on a markup language to describe the electrocardiogram (ecgML).