This dissertation based on a case study explores the acquisition and the guidance of Swedish Sign Language and spoken Swedish over a span of seven years. Interactions between a pair of fraternal twins, one deaf and one hearing, and their Deaf[1] family were video-observed within the home setting. The thesis consists of a frame which provides an overview of the relationship between four studies. These describe and analyze mainly storytime sessions over time. The first article addresses attentional expressions between the participants; the second article studies the mediation of the deaf twin’s first language acquisition; the third article analyses the hearing twins acquisition of parallel bimodal bilingualism; the fourth article concerns second language acquisition, sequential bimodal bilingualism following a cochlear implant (CI). In the frame, theoretical underpinnings such as mediation and language acquisition were compiled, within a sociocultural frame. This synthesis of results provides important information; in the 12- and 13-month sessions simultaneous-tactile-looking was noted in interchanges between the twins and their mother; mediation of bilingualism was scaffolded by the caregivers with the hearing twin by inserting single vocal words or signs into the language base used at that time, a finding that differs from other reported studies; a third finding is the simultaneousness in which the deaf child’s Swedish Sign Language skill worked as a cultural tool, to build a second and spoken language. The findings over time revealed actions that included all the family members. Irrespective of the number of modes and varied types of communication with more than one child, mediation included following-in the child’s initiation, intersubjective meaningfulness and encouragement. In accordance with previous research, these factors seem to promote the acquisition of languages. In conclusion, these findings should also prove useful in the more general educational field. [1] Deaf with a capital ‘D’ is commonly used for cultural affiliation whereas lower case ‘d’, as in deaf, refers to audiological status (Monaghan, Schmaling, Nakamura &amp; Turner, 2003). / <p>Disputationen tolkas till svensk teckenspråk, hörselslinga finns.</p><p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 3: Accepted. Paper 4: Submitted.</p>