The design of California's Structured English Immersion (SEI) program for limited-English-speaking students, which replaced its bilingual education program by state mandate, is described and suggestions for implementation are offered. SEI has several variations, each characterized by (1) extensive use of English and (2) use of English-as-a-Second-Language (ESL) methodology, which differs from mainstream English instruction. The report discusses differences between SEI, bilingual education, and sink-or-swim English language programs, research evidence supporting the effectiveness of SEI in different states and settings, the reasons for this effectiveness, factors to be considered in choosing SEI, and how to put together an SEI program, using examples from existing program designs. A study of SEI's use in Seattle (Washington) public schools is appended. (Contains 6 tables and 39 endnotes.) (MSE)