The patron saint of Issime is Saint James, called Sent Joapuk in the local variant of the Walser language, Töitschu, celebrated on 25 July, with the patronal feast held in the last week of the month. The parish church dedicated to him, in the hamlet of Duarf, has fine frescoes of the Last Judgement, the Mysteries of the Rosary on the churchyard, a Romanesque-style baptismal font and above all a Baroque high altar, the second largest in the Aosta Valley after that of Antagnod, with 182 statues. Alongside it there is also a winter patronal feast dedicated to Saint Sebastian.
Issime is a town of Walser language and culture, distinguished from other Alpine communities by its multilingualism and the coexistence of two ethnic groups, German-speaking and Franco-Provençal-speaking: historically up to five linguistic varieties are counted, Töitschu, the patois of Gaby, Piedmontese, French and, more recently, Italian. On the promontory facing the parish church stands the Herrenhaus, «Lord's House» in German, an ancient stronghold of the Vallaise nobles dating from the 14th century.
