Nebbiolo (/ˌnɛbiˈoʊloʊ/, Italian: [nebˈbjɔːlo]; Piedmontese: nebieul [neˈbjøl]) is an Italian red wine grape variety predominantly associated with its native Piedmont region, where it makes the Denominazione di Origine Controllata e Garantita (DOCG) wines of Barolo, Barbaresco, Gattinara, Ghemme, and Roero, together with numerous DOC wines. Nebbiolo is thought to derive its name from the Italian nebbia or Piedmontese nebia, meaning 'fog'. During harvest, which generally takes place late in October, a deep, intense fog sets into the Langhe region where many Nebbiolo vineyards are located. Alternative explanations refer to the fog-like glaucous veil that forms over the berries as they reach maturity, or that perhaps the name is derived instead from the Italian word nobile, meaning 'noble'. Nebbiolo produces lightly-colored red wines which can be highly tannic in youth with scents of tar and roses. As they age, the wines take on a characteristic brick-orange hue at the rim of the glass and mature to reveal other aromas and flavours such as violets, tar, wild herbs, cherries, raspberries, truffles, tobacco, and prunes. Nebbiolo wines can require years of ageing to balance the tannins with other characteristics.

Ampelographers believe that Nebbiolo is indigenous to the Piedmont region, though there is some DNA evidence to suggest that it could have originated in the Valtellina area of northern Lombardy, just to the east. In the 1st century AD, Pliny the Elder noted the exceptional quality of the wine produced in the Pollentia region located northwest of what is now the Barolo DOCG zone. While Pliny does not explicitly name the grape responsible for these Pollenzo wines, his description of the wine bears similarities to later descriptions of Nebbiolo-based wines, making this potentially the first notation of wine made from Nebbiolo in the Piedmont region. The first explicit mention of Nebbiolo dates to 1268, in which a wine known as "nibiol" was described as growing in Rivoli near Turin. This was followed by a 1303 account of a producer in the Roero district described as having a barrel of "nebiolo" (sic). In the 1304 treatise Liber Ruralium Commodorum, the Italian jurist Pietro Crescenzi described wine made from "nubiola" as being of excellent quality. In the 15th century, statutes in the region of La Morra (in what is now the Barolo zone) demonstrated the high esteem that the Nebbiolo vine had in the area. According to these laws, the penalties for cutting down a Nebbiolo vine ranged from a heavy fine to having the right hand cut off or hanging for repeat offenders.

The grape first captured attention outside Piedmont in the 18th century, when the British were looking for alternative wine sources to Bordeaux due to prolonged political conflicts with the French. However, the lack of easy transport from Piedmont to London would keep the Piedmontese wine from having the enduring relationship with British connoisseurship that is associated with Bordeaux, port and sherry. Nonetheless, plantings of Nebbiolo continued to grow during the 19th century until the phylloxera epidemic hit. With vast swaths of vineyards devastated by the pest, some vineyard owners decided to replant with different grape varieties, with Barbera being a significant beneficiary. Today, Nebbiolo covers around 9% of Piedmont vineyards, compared to the 30% occupied by Barbera.

In 2004, research at the University of California-Davis and Istituto Agrario di San Michele all’Adige found Nebbiolo to be related to Piedmont by way of two aromatic grape varieties – the Freisa grape of Piedmont and the French Rhone variety Viognier. This research further suggests a parent-offspring relationship between Nebbiolo and several Italian grapes including Freisa, Bubbierasco, Nebbiolo Rosé, and Vespolina of the Piedmont region, and the Lombardy grapes Negrara and Rossola nera. Additional DNA analysis also suggest a parent-offspring relationship with the Lombardy grape Brugnola, previously thought to be only a synonym for the Emilia-Romagna grape Fortana.

Compared to the annual growth cycle of other Piedmontese grape varieties, Nebbiolo is one of the first varieties to bud and the last variety to ripen with harvest taking place in mid to late October. In some vintages, producers are able to pick and complete fermentation of their Barbera and Dolcetto plantings before Nebbiolo is even harvested. To aid in ripening, producers will often plant Nebbiolo in the most favoured sites on south and southwestern-facing slopes, which give the grape more access to direct sunlight. The most ideal location is at an elevation between 150 and 300 meters (500 and 1,000 ft) and must provide some natural shelter from wind. The vine is very susceptible to coulure, especially if there is wet weather during budbreak or flowering. While rains during this period can affect yield and quantity, rains that occur after the period of veraison can have a detrimental effect on quality. The most highly rated bottles of Piedmont Nebbiolo tend to come from vintages that had dry weather during September and October. Nebbiolo needs sufficient warmth to develop the sugars and fruit flavours needed to balance the grape's naturally high acidity and tannins. In cooler climate areas, such as the subalpine regions of Carema, Valtellina and Donnaz, the grape will produce medium bodied wines with bracing acidity and tannins that need the benefit of a warm vintage.

Nebbiolo does not adapt particularly well to various vineyard soil types, preferring soils with high concentrations of calcareous marl such as those found on the right bank of the Tanaro river around Alba where Barolo and Barbaresco are produced. The grape can thrive in sandy soils, such as those on the left bank of the Tanaro around the Roero district but the wines from this soil type tend not to be as perfumed – lacking in particular the classic tar aromas. The slightly acidic pH of the sandy Roero soils tend to produce early maturing wines. The lighter wines of Ghemme and Gattinara come from the acidic porphyry soils of the hills between Novara and Vercelli. In the lower Aosta Valley, the soil has a high concentration of granite while the soils of the Valtellina region of Lombardy are predominantly schist based. In addition to soil type, the drainage ability and concentration of magnesium and potassium can have an influencing effect on the type of Nebbiolo wine produced.

Like many varieties (such as Pinot noir) with ancient pedigree, the Nebbiolo vine is genetically unstable and prone to mutation. As of 2001, there were around 40 different clones of Nebbiolo identified. The three main phenotypes used for winemaking are Lampia, Michet and Nebbiolo Rosé.

While Nebbiolo Rosé was originally thought to be a Nebbiolo clone, DNA research has later shown it to be a separate grape variety that has a parent-offspring relationship with Nebbiolo. Although the DOCG regulations for Barolo and Barbaresco require the wines to be made from Nebbiolo only, Nebbiolo Rosé remains permitted in practice. Its impact is limited by the fact that Nebbiolo Rosé had fallen out of favour long before the discovery that it was a separate variety, due, in part, to its wine's light colouring. Consequently, Nebbiolo Rosé accounts for only a small percentage of the vines grown for the production of Barolo and Barbaresco. Moreover, there are only a few bottlings where its presence is known to be significant.