Plastic, the main component of marine litter, is now ubiquitous in the marine environment. Ingestion of floating plastics is an emerging threat to seabirds, particularly for those already threatened. It is estimated that around 40% of the seabird species ingest plastic, which may cause wounds, intestinal blockage, decrease in feeding capacity, starvation and even death. Here, we aim to characterize the temporal trends and types of plastics ingested by seabirds in the Mediterranean Sea. For that, we assessed the plastic ingestion of 386 individuals from 10 species of Mediterranean seabirds: 113 Scopoli's (Calonectris diomedea), 68 Mediterranean (Puffinus yelkouan) and, 74 Balearic (P. mauretanicus) shearwaters, 42 Audouin's (Ichthyaetus audouinii), 12 Mediterranean (I. melanocephalus), 12 black-headed (Chroicocephalus ridibundus) and 43 yellow-legged (Larus michahellis) gulls, 4 black-legged kittiwakes (Rissa tridactyla), 16 Northern gannets (Morus bassanus) and 2 great skuas (Catharacta skua). Furthermore, we characterized the plastic polymer found using a Fourier-transform infrared spectrophotometer (FTIR). Seabirds included in the study were accidentally caught by longliners operating through the Catalan Coast, in the Western Mediterranean Sea from 2003 to 2014. Our results support recent findings of a higher occurrence of plastic ingestion in the three shearwaters than in the remaining study species. Scopoli's shearwaters showed higher occurrence (73.5%) and larger number of plastics (on average 7.0 ± 11.7) than Balearic (40.5%, 2.7 ± 1.4) and Mediterranean shearwaters (38.2%, 3.1 ± 4.8). The number of plastics ingested by shearwaters decreased from 2003 to 2014, but the total plastic mass accumulated did not change. The main plastic components found were polyethylene and polypropylene and did not differ among species. The proportion of each of these polymers resembled those found in surface waters of the NW Mediterranean. Thus, our results highlight the sensitivity of shearwaters to plastic ingestion and their suitability as sentinels for monitoring floating plastic pollution.