The main purpose of the study is to assess the long-term tolerability and effectiveness of lebrikizumab in adult and adolescent participants with moderate-to-severe atopic dermatitis (AD). Participants who complete the last assessment visit in ADjoin (Week 100) will be offered the opportunity to enroll in this extension study.

Inclusion Criteria:

1. Participants who completed treatment with lebrikizumab in ADjoin and their last participant assessment visit (Week 100) in that study.

2. For WOCBP: agree to remain abstinent (refrain from heterosexual intercourse) or use a highly effective contraceptive method during the treatment period and for at least 4 weeks after the last dose of lebrikizumab.

   NOTE: A WOCBP is defined as a postmenarcheal female, who has not reached a postmenopausal state (>=12 continuous months of amenorrhea with no identified cause other than menopause) and has not undergone surgical sterilization (removal of ovaries, fallopian tubes, and/or uterus).

   NOTE: The following are highly effective contraceptive methods: combined (estrogen and progestogen containing) hormonal contraception (oral, intravaginal, transdermal) associated with inhibition of ovulation, progestogen-only hormonal contraception (oral, injectable, implantable) associated with inhibition of ovulation, intrauterine device, intrauterine hormone-releasing system, bilateral tubal occlusion, bilateral tubal ligation, vasectomized partner, or sexual abstinence. In the context of this protocol, sexual abstinence is considered a highly effective method only if defined as refraining from heterosexual intercourse during the entire period of risk associated with the study treatments. The reliability of sexual abstinence should be evaluated in relation to the duration of the clinical trial and the preferred and usual lifestyle of the participant. Periodic abstinence (e.g., calendar, ovulation, symptothermal, or post ovulation methods) and withdrawal are not acceptable methods of contraception.

3. Ability to understand the purpose and risks of the trial, willingness and ability to comply with the protocol and provide written informed consent/assent in accordance with institutional and regulatory guidelines.

4. Capable of giving signed informed consent/assent as described in which includes compliance with the requirements and restrictions listed in the informed consent form (ICF) and in this protocol.

Exclusion Criteria:

1. Participants who, having participated in ADjoin, had their last lebrikizumab dose administered in a window longer than 8 weeks prior to the Baseline Visit in the current study.
2. Participants who, during their participation in the parent trial or ADjoin, developed an SAE or a severe AE that was deemed related to lebrikizumab, which in the opinion of the Investigator or of the medical monitor could indicate that continued treatment with lebrikizumab may present an unreasonable risk for the participant.
3. Conditions in the parent study or ADjoin consistent with protocol-defined criteria for permanent study drug discontinuation, if deemed related to lebrikizumab or led to Investigator or Sponsor-initiated withdrawal of participant from the study (e.g., non-compliance, inability to complete study assessments, etc.).
4. Treatment with a live (attenuated) vaccine from the time of last lebrikizumab dose in ADjoin prior to enrolment in the current study or planned during the study.
5. Use of a prohibited medication from the time of last lebrikizumab dose in ADjoin prior to enrolment in the current study or planned during the study.
6. Pregnant or breastfeeding women, and women planning to become pregnant or breastfeed during the study and for at least 4 weeks after the last dose of lebrikizumab.
7. Severe concomitant illness(es) that in the Investigator's judgment would adversely affect the participant's participation in the study. Any other medical or psychological condition that in the opinion of the Investigator may suggest a new and/or insufficiently understood disease, may present an unreasonable risk to the study patient because of his/her participation in this clinical trial, may make participant's participation unreliable, or may interfere with study assessments.
8. Any other conditions that, in the Investigator's opinion, might indicate the participant to be unsuitable for the trial.
9. Participant who is an employee or relative of an employee at the research site or Almirall.