Transcranial Doppler (TCD) ultrasonography is a non-invasive bedside tool applied to the assessment of cerebral blood flow haemodynamics in major intracranial arteries. TCD allows dynamic monitoring of vessel pulsatility, with a high temporal resolution, and it is relatively inexpensive, repeatable and portable. Two basic modalities are currently available in clinical practice for brain ultrasonography: transcranial Doppler (TCD) and brightness (B)-mode transcranial colour-coded duplex (TCCD), which represents an advancement of the TCD technique also allowing for the evaluation of brain structures. This chapter describes the principles behind the utilisation of both techniques as well as their derived parameters, indications, advantages and disadvantages.