In this dissertation, I investigate various aspects of object marking and how these manifest themselves in the signed modality. The main focus is on Swedish Sign Language (SSL), the national sign language of Sweden, which is the topic of investigation in all five studies. Two of the studies adopt a comparative perspective, including other sign languages as well. The studies comprise a range of data, including corpus data, elicited production, and acceptability judgments, and combine quantitative and qualitative methods in the analyses. The dissertation begins with an overview of the topics of valency, argument structure, and object marking, primarily from a spoken language perspective. Here, the interactions between semantics and morphosyntax are presented from a typological perspective, introducing differential object marking as a key concept. With regard to signed language, object marking is discussed in terms of both verbal and nominal strategies. Verbal strategies of object marking among sign languages include directional verbs, object handshape classifiers, and embodied perspective in signing. The first study investigates the use of directionality and object handshapes as object marking strategies in Al-Sayyid Bedouin Sign Language (ABSL), Israeli Sign Language (ISL), and SSL. It is shown that the strategies generally display different alignments in terms of the types of objects targeted, which is uniform across languages, but that directionality is much more marginal in ABSL than in the other two languages. Also, we see that there is a connection between object marking strategies and the animacy of the object, and that the strategies, object animacy, and word order preferences interact. In the second and third studies, SSL is investigated with regard to the transitive–reflexive distinction. Here, we see that there are interactional effects between object handshapes and the perspective taken by the signer. This points to intricate iconic motivations of combining and structuring complex verb sequences, such as giving preference to agent focusing structures (e.g., agent perspective and handling handshapes). Furthermore, the use of space is identified as a crucial strategy for reference tracking, especially when expressing semantically transitive events. Nominal strategies include object pronouns and derivations of the sign PERSON. The fourth study provides a detailed account of the object pronoun OBJPRO in SSL, which is the first in-depth description of this sign. It is found that the sign is in widespread use in SSL, often corresponds closely to object pronouns of spoken Swedish, and is argued to be grammaticalized from the lexical sign PERSON. In the final study, the possible existence of object pronouns in other sign languages is investigated by using a sample of 24 languages. This analysis reveals that the feature is found mostly in the Nordic countries, suggesting areal contact phenomena. However, the study also shows that there are a number of derivations of PERSON, such as reflexive pronouns, agreement auxiliaries, and case markers. The use of PERSON as a source of grammaticalization for these functions is attributed to both semantic and phonological properties of the sign. This dissertation is unique in that it is dedicated to the topic of object marking in the signed modality. It brings a variety of perspectives and methods together in order to investigate the domain of object marking, cross-linguistically and crossmodally. This is a doctoral thesis in Linguistics at Stockholm University, Sweden 2017.