Devanagari is a Northern Brahmic script related to many other South Asian scripts including Gujarati, Bengali, and Gurmukhi, and, more distantly, to a number of South-East Asian scripts including Thai, Balinese, and Baybayin. The script is used for over 120 spoken Indo-Aryan languages, including Hindi, Nepali, Marathi, Maithili, Awadhi, Newari and Bhojpuri. It is also used for writing Classical Sanskrit texts. Generally the orthography of the script reflects the pronunciation of the language.

The script is written from left to right. Letters hang from a headstroke, which is generally continuous throughout the length of the word, except when writing the letters jha, tha, dha, bha, a and ā, which all have a break in the headstroke. In handwriting, the headstroke is sometimes omitted.

Devanagari is an abugida; each letter represents a consonant with an inherent [ə] vowel, which can be modified using vowel diacritics. Vowel diacritics can be written above, below, to the left or to the right of the consonant. There are thirty-two consonant and ten vowel letters, plus ten vowel diacritics. The vowel signs represent long and short forms of five vowel sounds. Vowel sounds which are not preceded by a consonant are written with a vowel letter; otherwise they are indicated by a vowel diacritic, or, in the case of [ə], the lack thereof. There are also two letters for the long and short forms of the syllabic consonant [r̩], which are ordered with the vowel letters.

The Brahmic scripts are known for ordering the letters according to the principles of articulatory phonetics, that is, according to the place and manner in which the sound is produced. In Devanagari, the vowels are ordered first, with each short vowel followed by its long equivalent. The consonants are ordered by place, and within place, manner of articulation. Consonants are ordered in rows; velar, palatal, retroflex, dental, labial. Within each row, they follow the order unaspirated and aspirated voiceless, unaspirated and aspirated voiced, and nasal. Sonorants, fricatives and sibilants are ordered last.

Some letters take variant forms depending on their context. Notably, the letter ra takes different forms when in initial/final position, when preceding the letter ya, when preceding a consonant other than ya, when following a consonant with a vertical stem, and when following a letter with a rounded bottom.

Most consonants have two forms; a 'full' form and a 'half' form, which often visually resembles the full form but is missing the vertical stem. The half forms can combine with the full forms of other letters to represent consonant clusters. Those letters which don't have a half form make use of a halant symbol which silences the inherent vowel so that the two consonants can be pronounced in sequence. Some combinations join horizontally and some stack vertically. This is generally governed by the shape of the letter. A number of ligatures (commonly called conjuncts when referring to Indic scripts) are also used which do not bear visual similarity to the individual letters of which they are comprised.

Devanagari writing employs three non-alphabetic symbols for modifying the quality of a vowel. Anusvara is written with a dot above the vowel and either nasalizes the vowel or represents a nasal consonant articulated at the same place as the following consonant. A variant form of this symbol is called candrabindu and is written with a 'moon dot' above the letter to represent nasalization of the vowel exclusively. The symbol visarga follows anusvara; this symbol represents a voiceless breath following the vowel, and is written with two dots stacked vertically.