This chapter examines the organisational development of Na Fianna Éireann from their establishment in 1909 up to the 1916 Easter Rising. These seven years witnessed the slow and often unsteady development of the Fianna. During these years, Countess Constance Markievicz and Bulmer Hobson oversaw the emergence of a cadre of young Irish revolutionaries. The Fianna troops in Dublin city and county were the trailblazers within this increasingly republican youth group. Organisational changes in the Dublin area set the trend for those that would occur elsewhere. From their inception, the Fianna were in the military vanguard of the Irish nationalist movement through their provision of military training and promotion of a militant mindset. Thus, members were well prepared to assume an active role when the adult paramilitary organisations, the Irish Volunteers and the Irish Citizen Army, were formed in 1913. Serving and former Fianna members later played a prominent part in the 1916 Easter Rising, most famously Con Colbert and Sean Heuston who were executed for their roles in the rebellion.