Major linguistic work on Yagua includes:

    Payne, Thomas.  1992.  The Twins Stories:  Participant Coding in Yagua Narrative.  Berkeley:
            University of California Press.

    Powlison, Paul S.  1995.  Nijyami Niquejadamusi - May Niquejandamuju; May Niquejadamusy - Nijyami 
            Niquejadamuju (Diccionario Yagua-Castellano, Castellano-Yagua)
.  (Serie Linguitica Peruana No. 35.)
            Lima: Ministeio de Educacion y Instituto Linguistico de Verano.

My own research on Yagua, some of it co-authored with Tom Payne, was greatly facilitated by the pioneering work of Paul Powlison who shared with us an extensive text collection which he compiled during the 1950s and 1960s.  At the present time, most of these texts are in precarious physical condition and in a difficult form for almost any scholars and certainly for any native Yagua speakers to use.  However, they are extremely rich linguistically and culturally.